NASA Astrophysics Data System (ADS)
Nemov, A. S.; Boso, D. P.; Voynov, I. B.; Borovkov, A. I.; Schrefler, B. A.
2010-05-01
Superconducting coils are one of the key technical solutions used for generation of high magnetic field in modern tokamaks. Nb 3Sn superconductivity depends not only on temperature and magnetic field as e.g. NbTi, but also on the strain state of the strands inside the conductor. It is hence very important to be able to predict the mechanical deformations due to manufacturing processes and operating conditions. The conductors for ITER, the International Thermonuclear Experimental Reactor currently under construction, have a complex structure that makes analytical estimations of stiffness applicable only for the first cabling stages. In this work, a wide range of numerical simulations has been performed, by using several types of finite element models. This paper shows some analytical estimations for stretching and twisting and compares them with the numerical results of the different models. Some comparisons with experimental tests are also presented. Furthermore, it is shown that direct finite element analyses are compulsory for higher cable stages, but need the knowledge of the initial configuration as precise as possible for meaningful simulations. This problem is also addressed in this paper.
Stiffness and thermoelastic coefficients for composite laminates
NASA Technical Reports Server (NTRS)
Noor, Ahmed K.; Tenek, Lazarus H.
1992-01-01
Simple analytic expressions are presented for the stiffness and thermoelastic coefficients of composite laminates in terms of the material properties of the individual layers. Expressions for the derivatives of the various coefficients with respect to each of the material properties and fiber orientation angles are also included. For typical high-performance composites, numerical values are given showing the effects of the stacking sequence and the fiber orientation angle of quasi-isotropic and angle-ply laminates on the values of the various coefficients and their sensitivity derivatives. The expressions for the thermoelastic coefficients and the sensitivity derivatives are given herein for the first time.
Generalized Hansen Coefficients
NASA Astrophysics Data System (ADS)
Breiter, Sławomir; Métris, Gilles; Vokrouhlický, David
2004-02-01
Hansen coefficients X
Generalized Reflection Coefficients
NASA Astrophysics Data System (ADS)
Remling, Christian
2015-07-01
I consider general reflection coefficients for arbitrary one-dimensional whole line differential or difference operators of order 2. These reflection coefficients are semicontinuous functions of the operator: their absolute value can only go down when limits are taken. This implies a corresponding semicontinuity result for the absolutely continuous spectrum, which applies to a very large class of maps. In particular, we can consider shift maps (thus recovering and generalizing a result of Last-Simon) and flows of the Toda and KdV hierarchies (this is new). Finally, I evaluate an attempt at finding a similar general setup that gives the much stronger conclusion of reflectionless limit operators in more specialized situations.
Note on Two Generalizations of Coefficient Alpha.
ERIC Educational Resources Information Center
Raju, Nambury S.
1979-01-01
An important relationship is given for two generalizations of coefficient alpha: (1) Rajaratnam, Cronbach, and Gleser's generalizability formula for stratified-parallel tests, and (2) Raju's coefficient beta. (Author/CTM)
NASA Technical Reports Server (NTRS)
Della-Corte, Christopher
2012-01-01
Foil gas bearings are a key technology in many commercial and emerging oilfree turbomachinery systems. These bearings are nonlinear and have been difficult to analytically model in terms of performance characteristics such as load capacity, power loss, stiffness, and damping. Previous investigations led to an empirically derived method to estimate load capacity. This method has been a valuable tool in system development. The current work extends this tool concept to include rules for stiffness and damping coefficient estimation. It is expected that these rules will further accelerate the development and deployment of advanced oil-free machines operating on foil gas bearings.
NASA Technical Reports Server (NTRS)
DellaCorte, Christopher
2010-01-01
Foil gas bearings are a key technology in many commercial and emerging Oil-Free turbomachinery systems. These bearings are non-linear and have been difficult to analytically model in terms of performance characteristics such as load capacity, power loss, stiffness and damping. Previous investigations led to an empirically derived method, a rule-of-thumb, to estimate load capacity. This method has been a valuable tool in system development. The current paper extends this tool concept to include rules for stiffness and damping coefficient estimation. It is expected that these rules will further accelerate the development and deployment of advanced Oil-Free machines operating on foil gas bearings
NASA Astrophysics Data System (ADS)
Yang, G. L.; Zhang, L. Q.; Zhang, S. Y.
2012-11-01
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.
General dissipative coefficient in strong anisotropic inflation
NASA Astrophysics Data System (ADS)
Sharif, M.; Saleem, Rabia
2015-12-01
In this paper, we analyze the effects of generalized dissipative coefficient on the dynamics of warm intermediate and logamediate inflationary universe models during strong dissipative regime. We explore these models within the framework of locally rotationally symmetric Bianchi type I universe. In both cases, we evaluate inflaton, effective scalar potential, dissipative coefficient, slow-roll parameters, scalar and tensor power spectra, scalar spectral index and tensor-scalar ratio under slow-roll approximation. The inflationary model as well as perturbed parameters are constrained using recent data. We conclude that intermediate anisotropic inflationary universe model with generalized dissipative coefficient remains compatible with WMAP9, Planck and BICEP2 data while n=1 (arbitrary integer) is the only consistent case during logamediate era. Also, both of these models interpolate between weak and strong regimes.
Hansen Coefficients and Generalized Spherical Harmonics
NASA Astrophysics Data System (ADS)
Giacaglia, G. E. O.
Hansen's coefficients for the Fourier series in terms of the mean anomaly correspond to a rotation of the orbital plane proportional to the eccentricity of the orbit. Here, they are given in terms of Bessel functions and generalized associated Legendre functions. These functions arise naturally when one considers the transformation of spherical harmonics under rotation.
NASA Astrophysics Data System (ADS)
Ku, C.-P. Roger; Walton, James F., Jr.; Lund, Jorgen W.
1994-01-01
This paper provided an opportunity to quantify the angular stiffness and equivalent viscous damping coefficients of an axial spline coupling used in high-speed turbomachinery. A unique test methodology and data reduction procedures were developed. The bending moments and angular deflections transmitted across an axial spline coupling were measured while a nonrotating shaft was excited by an external shaker. A rotor dynamics computer program was used to simulate the test conditions and to correlate the angular stiffness and damping coefficients. In addition, sensitivity analyses were performed to show that the accuracy of the dynamic coefficients do not rely on the accuracy of the data reduction procedures.
NASA Technical Reports Server (NTRS)
Muravyov, Alexander A.
1999-01-01
In this paper, a method for obtaining nonlinear stiffness coefficients in modal coordinates for geometrically nonlinear finite-element models is developed. The method requires application of a finite-element program with a geometrically non- linear static capability. The MSC/NASTRAN code is employed for this purpose. The equations of motion of a MDOF system are formulated in modal coordinates. A set of linear eigenvectors is used to approximate the solution of the nonlinear problem. The random vibration problem of the MDOF nonlinear system is then considered. The solutions obtained by application of two different versions of a stochastic linearization technique are compared with linear and exact (analytical) solutions in terms of root-mean-square (RMS) displacements and strains for a beam structure.
NASA Astrophysics Data System (ADS)
Wei, Kai; Chen, Haosen; Pei, Yongmao; Fang, Daining
2016-01-01
The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CTEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications.
NASA Astrophysics Data System (ADS)
Kubrak, Elżbieta; Kubrak, Janusz; Kiczko, Adam
2015-10-01
The paper addresses the problem of determination of the energy and momentum coefficients for flows through a partly vegetated channel. These coefficients are applied to express the fluid kinetic energy and momentum equations as functions of a mean velocity. The study is based on laboratory measurements of water velocity distributions in a straight rectangular flume with stiff and flexible stems and plastic imitations of the Canadian waterweed. The coefficients were established for the vegetation layer, surface layer and the whole flow area. The results indicate that the energy and momentum coefficients increase significantly with water depth and the number of stems per unit channel area. New regression relationships for both coefficients are given.
Dynamic stiffness matrix of a rectangular plate for the general case
NASA Astrophysics Data System (ADS)
Banerjee, J. R.; Papkov, S. O.; Liu, X.; Kennedy, D.
2015-04-01
The dynamic stiffness matrix of a rectangular plate for the most general case is developed by solving the bi-harmonic equation and finally casting the solution in terms of the force-displacement relationship of the freely vibrating plate. Essentially the frequency dependent dynamic stiffness matrix of the plate when all its sides are free is derived, making it possible to achieve exact solution for free vibration of plates or plate assemblies with any boundary conditions. Previous research on the dynamic stiffness formulation of a plate was restricted to the special case when the two opposite sides of the plate are simply supported. This restriction is quite severe and made the general purpose application of the dynamic stiffness method impossible. The theory developed in this paper overcomes this long-lasting restriction. The research carried out here is basically fundamental in that the bi-harmonic equation which governs the free vibratory motion of a plate in harmonic oscillation is solved in an exact sense, leading to the development of the dynamic stiffness method. It is significant that the ingeniously sought solution presented in this paper is completely general, covering all possible cases of elastic deformations of the plate. The Wittrick-Williams algorithm is applied to the ensuing dynamic stiffness matrix to provide solutions for some representative problems. A carefully selected sample of mode shapes is also presented.
Linear equations in general purpose codes for stiff ODEs
Shampine, L. F.
1980-02-01
It is noted that it is possible to improve significantly the handling of linear problems in a general-purpose code with very little trouble to the user or change to the code. In such situations analytical evaluation of the Jacobian is a lot cheaper than numerical differencing. A slight change in the point at which the Jacobian is evaluated results in a more accurate Jacobian in linear problems. (RWR)
ERIC Educational Resources Information Center
Marsh, S. Neil
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
Non-monotonic dependence of the friction coefficient on heterogeneous stiffness.
Giacco, F; Ciamarra, M Pica; Saggese, L; de Arcangelis, L; Lippiello, E
2014-01-01
The complexity of the frictional dynamics at the microscopic scale makes difficult to identify all of its controlling parameters. Indeed, experiments on sheared elastic bodies have shown that the static friction coefficient depends on loading conditions, the real area of contact along the interfaces and the confining pressure. Here we show, by means of numerical simulations of a 2D Burridge-Knopoff model with a simple local friction law, that the macroscopic friction coefficient depends non-monotonically on the bulk elasticity of the system. This occurs because elastic constants control the geometrical features of the rupture fronts during the stick-slip dynamics, leading to four different ordering regimes characterized by different orientations of the rupture fronts with respect to the external shear direction. We rationalize these results by means of an energetic balance argument. PMID:25345800
Non-monotonic dependence of the friction coefficient on heterogeneous stiffness
Giacco, F.; Ciamarra, M. Pica; Saggese, L.; de Arcangelis, L.; Lippiello, E.
2014-01-01
The complexity of the frictional dynamics at the microscopic scale makes difficult to identify all of its controlling parameters. Indeed, experiments on sheared elastic bodies have shown that the static friction coefficient depends on loading conditions, the real area of contact along the interfaces and the confining pressure. Here we show, by means of numerical simulations of a 2D Burridge-Knopoff model with a simple local friction law, that the macroscopic friction coefficient depends non-monotonically on the bulk elasticity of the system. This occurs because elastic constants control the geometrical features of the rupture fronts during the stick-slip dynamics, leading to four different ordering regimes characterized by different orientations of the rupture fronts with respect to the external shear direction. We rationalize these results by means of an energetic balance argument. PMID:25345800
Non-monotonic dependence of the friction coefficient on heterogeneous stiffness
NASA Astrophysics Data System (ADS)
Giacco, F.; Ciamarra, M. Pica; Saggese, L.; de Arcangelis, L.; Lippiello, E.
2014-10-01
The complexity of the frictional dynamics at the microscopic scale makes difficult to identify all of its controlling parameters. Indeed, experiments on sheared elastic bodies have shown that the static friction coefficient depends on loading conditions, the real area of contact along the interfaces and the confining pressure. Here we show, by means of numerical simulations of a 2D Burridge-Knopoff model with a simple local friction law, that the macroscopic friction coefficient depends non-monotonically on the bulk elasticity of the system. This occurs because elastic constants control the geometrical features of the rupture fronts during the stick-slip dynamics, leading to four different ordering regimes characterized by different orientations of the rupture fronts with respect to the external shear direction. We rationalize these results by means of an energetic balance argument.
Antitrace Maps and Light Transmission Coefficients for Generalized Fibonacci Multilayers
NASA Astrophysics Data System (ADS)
Wang, Xiao-Guang; Pan, Shao-Hua; Yang, Guo-Zhen
2001-01-01
By using antitrace map method, we investigate the light transmission for a generalized Fibonacci multilayers. Analytical results are obtained for transmission coefficients in some special cases. We find that the transmission coefficients possess two-cycle property or six-cycle property. The cycle properties of the trace and antitrace are also obtained.
Note on the Generalized Hansen and Laplace Coefficients
NASA Astrophysics Data System (ADS)
Laskar, Jacques
2005-03-01
Recently, Breiter et al. [Celest. Mech. Dyn. Astron., 2004, 88, 153 161] reported the computation of Hansen coefficients X
NASA Astrophysics Data System (ADS)
Toro, Eleuterio F.; Montecinos, Gino I.
2015-12-01
We present a semi-analytical, implicit solution to the generalized Riemann problem (GRP) for non-linear systems of hyperbolic balance laws with stiff source terms. The solution method is based on an implicit, time Taylor series expansion and the Cauchy-Kowalewskaya procedure, along with the solution of a sequence of classical Riemann problems. Our new GRP solver is then used to construct locally implicit ADER methods of arbitrary accuracy in space and time for solving the general initial-boundary value problem for non-linear systems of hyperbolic balance laws with stiff source terms. Analysis of the method for model problems is carried out and empirical convergence rate studies for suitable tests problems are performed, confirming the theoretically expected high order of accuracy.
NASA Technical Reports Server (NTRS)
Thomson, Robert G.
1959-01-01
A study has been made of the effects of varying the shape, solidity, and heat-transfer coefficient of thin wings with regard to their influence on the torsional-stiffness reduction induced by aerodynamic heating. The variations in airfoil shape include blunting, flattening, and combined blunting and flattening of a solid wing of symmetrical double-wedge cross section. Hollow double-wedge wings of constant skin thickness with and without internal webs also are considered. The effects of heat-transfer coefficients appropriate for laminar and turbulent flow are investigated in addition to a step transition along the chord from a lower to a higher constant value of heat-transfer coefficient. From the results given it is concluded that the flattening of a solid double wedge decreases the reduction in torsional stiffness while slight degrees of blunting increase the loss. The influence of chordwise variations in heat-transfer coefficient due to turbulent and laminar boundary-layer flow on the torsional stiffness of solid wings is negligible. The effect of a step transition in heat-transfer coefficient along the chord of a solid wing can, however, become appreciable. The torsional-stiffness reduction of multiweb and hollow double-wedge wings is substantially less than that calculated for a solid wing subjected to the same heating conditions.
Generalized transport coefficients for inelastic Maxwell mixtures under shear flow
NASA Astrophysics Data System (ADS)
Garz, Vicente; Trizac, Emmanuel
2015-11-01
The Boltzmann equation framework for inelastic Maxwell models is considered to determine the transport coefficients associated with the mass, momentum, and heat fluxes of a granular binary mixture in spatially inhomogeneous states close to the simple shear flow. The Boltzmann equation is solved by means of a Chapman-Enskog-type expansion around the (local) shear flow distributions fr(0 ) for each species that retain all the hydrodynamic orders in the shear rate. Due to the anisotropy induced by the shear flow, tensorial quantities are required to describe the transport processes instead of the conventional scalar coefficients. These tensors are given in terms of the solutions of a set of coupled equations, which can be analytically solved as functions of the shear rate a , the coefficients of restitution ?r s, and the parameters of the mixture (masses, diameters, and composition). Since the reference distribution functions fr(0 ) apply for arbitrary values of the shear rate and are not restricted to weak dissipation, the corresponding generalized coefficients turn out to be nonlinear functions of both a and ?r s. The dependence of the relevant elements of the three diffusion tensors on both the shear rate and dissipation is illustrated in the tracer limit case, the results showing that the deviation of the generalized transport coefficients from their forms for vanishing shear rates is in general significant. A comparison with the previous results obtained analytically for inelastic hard spheres by using Grad's moment method is carried out, showing a good agreement over a wide range of values for the coefficients of restitution. Finally, as an application of the theoretical expressions derived here for the transport coefficients, thermal diffusion segregation of an intruder immersed in a granular gas is also studied.
Inflationary weak anisotropic model with general dissipation coefficient
NASA Astrophysics Data System (ADS)
Sharif, M.; Saleem, Rabia
2016-03-01
This paper explores the dynamics of warm intermediate and logamediate inflationary models during weak dissipative regime with a general form of dissipative coefficient. We analyze these models within the framework of locally rotationally symmetric Bianchi type I universe. In both cases, we evaluate solution of inflaton, effective scalar potential, dissipative coefficient, slow-roll parameters, scalar and tensor power spectra, scalar spectral index and tensor to scalar ratio under slow-roll approximation. We constrain the model parameters using recent data and conclude that anisotropic inflationary universe model with generalized dissipation coefficient remains compatible with WMAP9, Planck and BICEP2 data. Finally, we have checked the effects of bulk viscous pressure on this considered model and found that it remains compatible with recent data only for intermediate case.
NASA Astrophysics Data System (ADS)
Zhou, Jin; Di, Long; Cheng, Changli; Xu, Yuanping; Lin, Zongli
2016-01-01
The stiffness and damping coefficients of active magnetic bearings (AMBs) have direct influence on the dynamic response of a rotor bearing system, including the bending critical speeds, modes of vibrations and stability. Rotor unbalance response is informative in the identification of these bearing support parameters. In this paper, we propose a method for identifying closed-loop AMB stiffness and damping coefficients based on the rotor unbalance response. We will use a flexible rotor-AMB test rig to help describe the proposed method as well as to validate the identification results. First, based on a rigid body model of the rotor, a formula is derived that computes the nominal values of the bearing stiffness and damping coefficients at a given rotating speed from the experimentally measured rotor unbalance response at the given speed. Then, based on a finite element model of the rotor, an error response surface is constructed for each parameter to estimate the identification errors induced by the rotor flexibility. The final identified values of the stiffness and damping coefficients equal the sums of the nominal values initially computed from the unbalance response and the identification errors determined by the error response surfaces. The proposed identification method is carried out on the rotor-AMB test rig. In order to validate the identification results, the identified values of the closed-loop AMB stiffness and damping coefficients are combined with the finite element model of the rotor to form a full model of the rotor-AMB test rig, from which the model unbalance responses at various rotating speeds are determined through simulation and compared with the experimental measurements. The close agreements between the simulation results and the measurements validate the proposed identification method.
Generalized drag coefficient applicable for all flow regimes
Meyer, B.R.
1986-05-26
A generalized drag coefficient correlation for particulate settling in power-law-type fluids is applicable for all flow regimes from Stokes' (laminar) to Newton's flow (turbulence). The major advantage of this correlation for hydrocarbon reservoirs is that it correctly asymptotes to a modified Stokes' law (viscous effects) at low Reynolds value (Re) numbers and to the turbulent drag coefficient C/sub D/ approx. = 0.44 at large values of Re (inertia dominance). The use of Stokes' law can greatly underestimate the drag coefficient and grossly overestimate the terminal settling velocity at large Re. In many respects, this article is a review and extension of drag coefficient correlations used in hydraulic fracturing on particulate settling in Newtonian and non-Newtonian fluids. Since most non-Newtonian correlations are for creeping flow (Re' < 0.1), the major emphasis will be to extend these correlations to Newton's flow. A comparison with experimental data and empirical correlations of other investigators is included to verify the validity and applicability of the extended correlation.
Second virial coefficient of a generalized Lennard-Jones potential.
González-Calderón, Alfredo; Rocha-Ichante, Adrián
2015-01-21
We present an exact analytical solution for the second virial coefficient of a generalized Lennard-Jones type of pair potential model. The potential can be reduced to the Lennard-Jones, hard-sphere, and sticky hard-sphere models by tuning the potential parameters corresponding to the width and depth of the well. Thus, the second virial solution can also regain the aforementioned cases. Moreover, the obtained expression strongly resembles the one corresponding to the Kihara potential. In fact, the Fk functions are the same. Furthermore, for these functions, the complete expansions at low and high temperature are given. Additionally, we propose an alternative stickiness parameter based on the obtained second virial coefficient. PMID:25612707
Stiffness jump in the generalized XY model on the square lattice.
Hübscher, David M; Wessel, Stefan
2013-06-01
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
GYutsis: heuristic based calculation of general recoupling coefficients
NASA Astrophysics Data System (ADS)
Van Dyck, D.; Fack, V.
2003-08-01
General angular momentum recoupling coefficients can be expressed as a summation formula over products of 6- j coefficients. Yutsis, Levinson and Vanagas developed graphical techniques for representing the general recoupling coefficient as a cubic graph and they describe a set of reduction rules allowing a stepwise generation of the corresponding summation formula. This paper is a follow up to [Van Dyck and Fack, Comput. Phys. Comm. 151 (2003) 353-368] where we described a heuristic algorithm based on these techniques. In this article we separate the heuristic from the algorithm and describe some new heuristic approaches which can be plugged into the generic algorithm. We show that these new heuristics lead to good results: in many cases we get a more efficient summation formula than our previous approach, in particular for problems of higher order. In addition the new features and the use of our program GYutsis, which implements these techniques, is described both for end users and application programmers. Program summaryTitle of program: CycleCostAlgorithm, GYutsis Catalogue number: ADSA Program Summary URL:http://cpc.cs.qub.ac.uk/summaries/ADSA Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland. Users may obtain the program also by downloading either the compressed tar file gyutsis.tgz (for Unix and Linux) or the zip file gyutsis.zip (for Windows) from our website ( http://caagt.rug.ac.be/yutsis/). An applet version of the program is also available on our website and can be run in a web browser from the URL http://caagt.rug.ac.be/yutsis/GYutsisApplet.html. Licensing provisions: none Computers for which the program is designed: any computer with Sun's Java Runtime Environment 1.4 or higher installed. Programming language used: Java 1.2 (Compiler: Sun's SDK 1.4.0) No. of lines in program: approximately 9400 No. of bytes in distributed program, including test data, etc.: 544 117 Distribution format: tar gzip file Nature of physical problem: A general recoupling coefficient for an arbitrary number of (integer or half-integer) angular momenta can be expressed as a formula consisting of products of 6- j coefficients summed over a certain number of variables. Such a formula can be generated using the program GYutsis (with a graphical user front end) or CycleCostAlgorithm (with a text-mode user front end). Method of solution: Using the graphical techniques of Yutsis, Levinson and Vanagas (1962) a summation formula for a general recoupling coefficient is obtained by representing the coefficient as a Yutsis graph and by performing a selection of reduction rules valid for such graphs. Each reduction rule contributes to the final summation formula by a numerical factor or by an additional summation variable. Whereas an optimal summation formula (i.e. with a minimum number of summation variables) is hard to obtain, we present here some new heuristic approaches for selecting an edge from a k-cycle in order to transform it into an ( k-1)-cycle ( k>3) in such a way that a 'good' summation formula is obtained. Typical running time: From instantaneously for the typical problems to 30 s for the heaviest problems on a Pentium II-350 Linux-system with 256 MB RAM.
Aerodynamic coefficients in generalized unsteady thin airfoil theory
NASA Technical Reports Server (NTRS)
Williams, M. H.
1980-01-01
Two cases are considered: (1) rigid body motion of an airfoil-flap combination consisting of vertical translation of given amplitude, rotation of given amplitude about a specified axis, and rotation of given amplitude of the control surface alone about its hinge; the upwash for this problem is defined mathematically; and (2) sinusoidal gust of given amplitude and wave number, for which the upwash is defined mathematically. Simple universal formulas are presented for the most important aerodynamic coefficients in unsteady thin airfoil theory. The lift and moment induced by a generalized gust are evaluated explicitly in terms of the gust wavelength. Similarly, in the control surface problem, the lift, moment, and hinge moments are given as explicit algebraic functions of hinge location. These results can be used together with any of the standard numerical inversion routines for the elementary loads (pitch and heave).
Generalized semiparametric varying-coefficient models for longitudinal data
NASA Astrophysics Data System (ADS)
Qi, Li
In this dissertation, we investigate the generalized semiparametric varying-coefficient models for longitudinal data that can flexibly model three types of covariate effects: time-constant effects, time-varying effects, and covariate-varying effects, i.e., the covariate effects that depend on other possibly time-dependent exposure variables. First, we consider the model that assumes the time-varying effects are unspecified functions of time while the covariate-varying effects are parametric functions of an exposure variable specified up to a finite number of unknown parameters. The estimation procedures are developed using multivariate local linear smoothing and generalized weighted least squares estimation techniques. The asymptotic properties of the proposed estimators are established. The simulation studies show that the proposed methods have satisfactory finite sample performance. ACTG 244 clinical trial of HIV infected patients are applied to examine the effects of antiretroviral treatment switching before and after HIV developing the 215-mutation. Our analysis shows benefit of treatment switching before developing the 215-mutation. The proposed methods are also applied to the STEP study with MITT cases showing that they have broad applications in medical research.
NASA Astrophysics Data System (ADS)
Goren, L.; Aharonov, E.; Sparks, D.; Toussaint, R.
2010-09-01
The physics of deformation of fluid-filled granular media controls many geophysical systems, ranging from shear on geological faults to landslides and soil liquefaction. Its great complexity is rooted in the mechanical coupling between two deforming phases: the solid granular network and the fluid-filled pore network. Often deformation of the granular network leads to pore fluid pressure (PP) changes. If the PP rises enough, the fluid-filled granular media may transition from a stress-supporting grain network to a flowing grain-fluid slurry, with an accompanying catastrophic loss of shear strength. Despite its great importance, the mechanisms and parameters controlling PP evolution by granular shear are not well understood. A formulation describing the general physics of pore fluid response to granular media deformation is developed and used to study simple scenarios that lead to PP changes. We focus on the infinitely stiff end-member scenario, where granular deformation is prescribed, and the PP responds to this deformation. This end-member scenario illustrates the two possible modes of pore fluid pressurization: (1) via rapid fluid flow when fluid drainage is good and (2) via pore volume compaction when drainage is poor. In the former case the rate of deformation controls PP evolution, while in the latter case, fluid compressibility is found to be an important parameter and the amount of pressurization is controlled by the overall compaction. The newly suggested fluid-induced mechanism (mechanism 1) may help explain observations of liquefaction of initially compact soils and shear zones.
Alvim, R O; Santos, P C J L; Ferreira, N E; Mill, J G; Krieger, J E; Pereira, A C
2012-05-01
Thioredoxin interacting protein plays a pivotal role in several important processes of cardiovascular homeostasis by functioning as a biological sensor for biomechanical and oxidative stress. However, the effects of genetic variants in the modulation of arterial stiffness are unknown. In this scenario, the present study evaluated the relationship between the TXNIP rs7212 polymorphism and arterial stiffness. In the overall sample and in the diabetic group, individuals carrying CG+GG genotypes had higher PWV values compared with CC genotype group (10.0 vs 9.8?m?s (-1), P=0.03; 12.3 vs 11.2?m?s(-1), P=0.01; respectively). Our findings indicated that the G allele may contribute to increased arterial stiffness in the Brazilian general population and suggest a possible interaction with diabetes. PMID:22113441
Fan, Li; Ye, Ping; Yuan, Ying; Lu, XueChun; Wang, Fan; Zeng, Qiang
2013-01-01
Background Some cardiovascular risk factors have been confirmed to be positively correlated with arterial stiffness. However, it is unclear whether HDL-C, a well-established anti-risk factor, has an independent association with arterial stiffness. The aim of this study was to evaluate the relationship between HDL-C levels and arterial stiffness and the possible role of high-sensitivity C-reactive protein (hs-CRP) in this potential correlation in apparently healthy adults undergoing a general health examination in China. Materials and Methods This was a cross-sectional survey. In total, 15,302 participants (age range, 1882 years; mean, 43.888.44 years) were recruited during routine health status examinations. A questionnaire was used and we measured the body mass index, systolic and diastolic blood pressure, and fasting glucose, and serum lipid, uric acid, hs-CRP, and serum creatinine levels of each participant. Central arterial stiffness was assessed by carotidfemoral pulse wave velocity (cf-PWV). Results HDL-C levels decreased as cf-PWV increased. Pearsons correlation analysis revealed that HDL-C levels were associated with cf-PWV (r=?0.18, P<0.001). hs-CRP levels were positively associated with cf-PWV (r=0.13). After adjustment for all confounders, HDL-C was inversely independently associated with all quartiles of cf-PWV. Furthermore, HDL-C was associated with cf-PWV in different quartiles of hs-CRP, and the correlation coefficients (r) gradually decreased with increasing hs-CRP levels (quartiles 14). Conclusions HDL-C is inversely independently associated with central arterial stiffness. The anti-inflammatory activity of HDL-C may mediate its relationship with cf-PWV. Further, long-term follow-up studies are needed to evaluate whether high HDL-C levels are protective against central artery stiffening through the anti-inflammatory activity of HDL-C. PMID:24312587
NASA Astrophysics Data System (ADS)
Arboleda-Monsalve, Luis G.; Zapata-Medina, David G.; Aristizabal-Ochoa, J. Daro
2008-03-01
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.
General dissipation coefficient in low-temperature warm inflation
Bastero-Gil, Mar; Berera, Arjun; Rosa, João G.; Ramos, Rudnei O. E-mail: ab@ph.ed.ac.uk E-mail: joao.rosa@ed.ac.uk
2013-01-01
In generic particle physics models, the inflaton field is coupled to other bosonic and fermionic fields that acquire large masses during inflation and may decay into light degrees of freedom. This leads to dissipative effects that modify the inflationary dynamics and may generate a nearly-thermal radiation bath, such that inflation occurs in a warm rather than supercooled environment. In this work, we perform a numerical computation and obtain expressions for the associated dissipation coefficient in supersymmetric models, focusing on the regime where the radiation temperature is below the heavy mass threshold. The dissipation coefficient receives contributions from the decay of both on-shell and off-shell degrees of freedom, which are dominant for small and large couplings, respectively, taking into account the light field multiplicities. In particular, we find that the contribution from on-shell decays, although Boltzmann-suppressed, can be much larger than that of virtual modes, which is bounded by the validity of a perturbative analysis. This result opens up new possibilities for realizations of warm inflation in supersymmetric field theories.
Ecological optimization and coefficient of performance bounds of general refrigerators
NASA Astrophysics Data System (ADS)
Long, Rui; Liu, Wei
2016-02-01
An analysis of COP and its bounds at maximum ecological criterion for general refrigerators is conducted. For generality, both the non-isothermal heat transfer processes and the internal dissipations are considered. Under different situations, the COP under the maximum ecological criterion have been studied systematically. And the general upper and lower bounds of the optimal COP have been obtained. Furthermore under maximum ecological criterion, the COP of general endoreversible refrigerators have also been studied. And the COP bounds of different kinds of refrigerators have been analyzed. As actual refrigerators may not operate under the condition of maximum COP or maximum cooling load, but operate under the maximum ecological condition which indicates the best compromise between the refrigeration rate and the loss of refrigeration rate. This paper could provide a practical insight for designing and operating actual refrigerators.
A Generalized Family of Coefficients of Relational Agreement for Numerical Scales.
ERIC Educational Resources Information Center
Fagot, Robert F.
1993-01-01
A family of coefficients of relational agreement for numerical scales is proposed, generalizing to multiple judges the theory of F. E. Zegers and J. M. F. ten Berge (1985) of association coefficients for two variables, using the premise that choice of coefficient depends on scale type of the variables. (SLD)
Judd, Linda J.; Asquith, William H.; Slade, Raymond M., Jr.
1996-01-01
This report presents two techniques to estimate generalized skew coefficients used for log-Pearson Type III peak-streamflow frequency analysis of natural basins in Texas. A natural basin has less than 10 percent impervious cover, and less than 10 percent of its drainage area is controlled by reservoirs. The estimation of generalized skew coefficients is based on annual peak and historical peak streamflow for all U.S. Geological Survey streamflow-gaging stations having at least 20 years of annual peak-streamflow record from natural basins in Texas. Station skew coefficients calculated for each of 255 Texas stations were used to estimate generalized skew coefficients for Texas. One technique to estimate generalized skew coefficients involved the use of regression equations developed for each of eight regions in Texas, and the other involved development of a statewide map of generalized skew coefficients. The weighted mean of the weighted mean standard errors of the regression equations for the eight regions is 0.36 log10 skew units, and the weighted mean standard error of the map is 0.35 log10 skew units. The technique based on the map is preferred for estimating generalized skew coefficients because of its smooth transition from one region of the State to another.
NASA Technical Reports Server (NTRS)
Bert, C. W.; Chang, S.
1972-01-01
Elastic and damping analyses resulting in determinations of the various stiffnesses and associated loss tangents for the complete characterization of the elastic and damping behavior of a monofilament composite layer are presented. For the determination of the various stiffnesses, either an elementary mechanics-of-materials formulation or a more rigorous mixed-boundary-value elasticity formulation is used. The solution for the latter formulation is obtained by means of the boundary-point least-square error technique. Kimball-Lovell type damping is assumed for each of the constituent materials. For determining the loss tangents associated with the various stiffnesses, either the viscoelastic correspondence principle or an energy analysis based on the appropriate elastic stress distribution is used.
Generalized Caroli formula for the transmission coefficient with lead-lead coupling.
Li, Huanan; Agarwalla, Bijay Kumar; Wang, Jian-Sheng
2012-07-01
We present a generalized transmission coefficient formula for the lead-junction-lead system, in which interaction between the leads has been taken into account. Based on this formula, the Caroli formula could be easily recovered and a transmission coefficient formula for interface problem in the ballistic system can be obtained. The condition of validity for the formula is carefully explored. We mainly focus on heat transport. However, the corresponding electrical transport could be similarly dealt with. Also, an illustrative example is given to clarify the precise meaning of the quantities used in the formula, such as the concept of the reduced interacting matrix in different situations. In addition, an explicit transmission coefficient formula for a general one-dimensional interface setup is obtained based on the derived interface formula. PMID:23005402
NASA Astrophysics Data System (ADS)
Lock, James A.
2013-09-01
The vector wave equation for electromagnetic waves, when subject to a number of constraints corresponding to propagation of a monochromatic beam, reduces to a pair of inhomogeneous differential equations describing the transverse electric and transverse magnetic polarized beam components. These differential equations are solved analytically to obtain the most general focused Gaussian beam to order s4, where s is the beam confinement parameter, and various properties of the most general Gaussian beam are then discussed. The radial fields of the most general Gaussian beam are integrated to obtain the on-axis beam shape coefficients of the generalized Lorenz-Mie theory formalism of light scattering. The beam shape coefficients are then compared with those of the localized Gaussian beam model and the Davis-Barton fifth-order symmetrized beam.
ERIC Educational Resources Information Center
Lai, Dejian; Huang, Jin; Risser, Jan M.; Kapadia, Asha S.
2008-01-01
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…
ERIC Educational Resources Information Center
Lai, Dejian; Huang, Jin; Risser, Jan M.; Kapadia, Asha S.
2008-01-01
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
Trial equation method for solving the generalized Fisher equation with variable coefficients
NASA Astrophysics Data System (ADS)
Triki, Houria; Wazwaz, Abdul-Majid
2016-03-01
We investigate a generalized Fisher equation with temporally varying coefficients, describing the dynamics of a field in inhomogeneous media. A class of exact soliton solutions of this equation is presented, and some of which are derived for the first time. The trial equation method is applied to obtain these soliton solutions. The constraint conditions for the existence of these solutions are also exhibited.
Coefficient of performance and its bounds with the figure of merit for a general refrigerator
NASA Astrophysics Data System (ADS)
Long, Rui; Liu, Wei
2015-02-01
A general refrigerator model with non-isothermal processes is studied. The coefficient of performance (COP) and its bounds at maximum ? figure of merit are obtained and analyzed. This model accounts for different heat capacities during the heat transfer processes. So, different kinds of refrigerator cycles can be considered. Under the constant heat capacity condition, the upper bound of the COP is the Curzon-Ahlborn (CA) coefficient of performance and is independent of the time durations of the heat exchanging processes. With the maximum ? criterion, in the refrigerator cycles, such as the reversed Brayton refrigerator cycle, the reversed Otto refrigerator cycle and the reversed Atkinson refrigerator cycle, where the heat capacity in the heat absorbing process is not less than that in the heat releasing process, their COPs are bounded by the CA coefficient of performance; otherwise, such as for the reversed Diesel refrigerator cycle, its COP can exceed the CA coefficient of performance. Furthermore, the general refined upper and lower bounds have been proposed.
Preacher, Kristopher J; Hancock, Gregory R
2015-03-01
A fundamental goal of longitudinal modeling is to obtain estimates of model parameters that reflect meaningful aspects of change over time. Often, a linear or nonlinear model may be sensible from a theoretical perspective, yet may have parameters that are difficult to interpret in a way that sheds light on substantive hypotheses. Fortunately, such models may be reparameterized to yield more easily interpretable parameters. This article has 3 goals. First, we provide theoretical background and elaboration on Preacher and Hancock's (2012) 4-step method for reparameterizing growth curve models. Second, we extend this method by providing a user-friendly modification of the structured latent curve model in the third step that enables fitting models that are not estimable with the original method. This modification also allows researchers to specify the mean structure without having to determine which parameters enter nonlinearly and without needing to solve complex matrix expressions. Third, we illustrate how this general reparameterization method allows researchers to treat the average rate of change, half-life, and knot (transition point) as random coefficients; these aspects of change have not before been treated as random coefficients in structural equation modeling. We supply Mplus code for illustrative examples in an online supplement. Our core message is that growth curve models are considerably more flexible than most researchers may suspect. Virtually any parameter can be treated as a random coefficient that varies across individuals. Alternative parameterizations of a given model may yield unique insights that are not available with traditional parameterizations. PMID:25822207
Williams, C.J.; Heglund, P.J.
2009-01-01
Habitat association models are commonly developed for individual animal species using generalized linear modeling methods such as logistic regression. We considered the issue of grouping species based on their habitat use so that management decisions can be based on sets of species rather than individual species. This research was motivated by a study of western landbirds in northern Idaho forests. The method we examined was to separately fit models to each species and to use a generalized Mahalanobis distance between coefficient vectors to create a distance matrix among species. Clustering methods were used to group species from the distance matrix, and multidimensional scaling methods were used to visualize the relations among species groups. Methods were also discussed for evaluating the sensitivity of the conclusions because of outliers or influential data points. We illustrate these methods with data from the landbird study conducted in northern Idaho. Simulation results are presented to compare the success of this method to alternative methods using Euclidean distance between coefficient vectors and to methods that do not use habitat association models. These simulations demonstrate that our Mahalanobis-distance- based method was nearly always better than Euclidean-distance-based methods or methods not based on habitat association models. The methods used to develop candidate species groups are easily explained to other scientists and resource managers since they mainly rely on classical multivariate statistical methods. ?? 2008 Springer Science+Business Media, LLC.
NASA Astrophysics Data System (ADS)
Weldon, W. F.; Bacon, J. L.; Weeks, D. A.; Zowarka, R. C., Jr.
1991-01-01
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.
Lue Xing; Zhang Haiqiang; Xu Tao; Li He; Tian Bo
2010-12-15
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.
L, Xing; Tian, Bo; Zhang, Hai-Qiang; Xu, Tao; Li, He
2010-12-01
Gardner model describes certain nonlinear elastic structures, ion-acoustic waves in plasmas, and shear flows in ocean and atmosphere. In this paper, by virtue of the computerized symbolic computation, the integrability of a generalized (2+1)-dimensional variable-coefficient Gardner model is investigated. Painleve? integrability conditions are derived among the coefficient functions, which reduce all the coefficient functions to be proportional only to ?(t), the coefficient of the cubic nonlinear term u(2)u(x). Then, an independent transformation of the variable t transforms the reduced ?(t)-dependent equation into a constant-coefficient integrable one. Painleve? test shows that this is the only case when our original generalized (2+1)-dimensional variable-coefficient Gardner model is integrable. PMID:21198095
Shujie, MA; Carroll, Raymond J.; Liang, Hua; Xu, Shizhong
2015-01-01
In the low-dimensional case, the generalized additive coefficient model (GACM) proposed by Xue and Yang [Statist. Sinica 16 (2006) 14231446] has been demonstrated to be a powerful tool for studying nonlinear interaction effects of variables. In this paper, we propose estimation and inference procedures for the GACM when the dimension of the variables is high. Specifically, we propose a groupwise penalization based procedure to distinguish significant covariates for the large p small n setting. The procedure is shown to be consistent for model structure identification. Further, we construct simultaneous confidence bands for the coefficient functions in the selected model based on a refined two-step spline estimator. We also discuss how to choose the tuning parameters. To estimate the standard deviation of the functional estimator, we adopt the smoothed bootstrap method. We conduct simulation experiments to evaluate the numerical performance of the proposed methods and analyze an obesity data set from a genome-wide association study as an illustration. PMID:26412908
NASA Astrophysics Data System (ADS)
Elnaggar, Sameh Y.; Tervo, Richard J.; Mattar, Saba M.
2015-11-01
The theory and operation of various devices and systems, such as wireless power transfer via magnetic resonant coupling, magneto-inductive wave devices, magnetic resonance spectroscopy probes, and metamaterials can rely on coupled tuned resonators. The coupling strength is usually expressed in terms of the coupling coefficient κ, which can have electrical κE and/or magnetic κM components. In the current article, general expressions of κ are derived. The relation between the complex Poynting equation in its microscopic form and κ is made and discussed in detail. It is shown that κ can be expressed in terms of the interaction energy between the resonators' modes. It thus provides a general form that combines the magnetic and electric components of κ. The expressions make it possible to estimate the frequencies and fields of the coupled modes for arbitrarily oriented and spaced resonators. Thus, enabling the calculation of system specific parameters such as the transfer efficiency of wireless power transfer systems, resonator efficiency for electron spin resonance probes, and dispersion relations of magneto-inductive and stereo-metamaterials structures.
A computer program for two-particle generalized coefficients of fractional parentage
NASA Astrophysics Data System (ADS)
Deveikis, A.; Juodagalvis, A.
2008-10-01
We present a FORTRAN90 program GCFP for the calculation of the generalized coefficients of fractional parentage (generalized CFPs or GCFP). The approach is based on the observation that the multi-shell CFPs can be expressed in terms of single-shell CFPs, while the latter can be readily calculated employing a simple enumeration scheme of antisymmetric A-particle states and an efficient method of construction of the idempotent matrix eigenvectors. The program provides fast calculation of GCFPs for a given particle number and produces results possessing numerical uncertainties below the desired tolerance. A single j-shell is defined by four quantum numbers, (e,l,j,t). A supplemental C++ program parGCFP allows calculation to be done in batches and/or in parallel. Program summaryProgram title:GCFP, parGCFP Catalogue identifier: AEBI_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBI_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 17 199 No. of bytes in distributed program, including test data, etc.: 88 658 Distribution format: tar.gz Programming language: FORTRAN 77/90 ( GCFP), C++ ( parGCFP) Computer: Any computer with suitable compilers. The program GCFP requires a FORTRAN 77/90 compiler. The auxiliary program parGCFP requires GNU-C++ compatible compiler, while its parallel version additionally requires MPI-1 standard libraries Operating system: Linux (Ubuntu, Scientific) (all programs), also checked on Windows XP ( GCFP, serial version of parGCFP) RAM: The memory demand depends on the computation and output mode. If this mode is not 4, the program GCFP demands the following amounts of memory on a computer with Linux operating system. It requires around 2 MB of RAM for the A=12 system at E⩽2. Computation of the A=50 particle system requires around 60 MB of RAM at E=0 and ˜70 MB at E=2 (note, however, that the calculation of this system will take a very long time). If the computation and output mode is set to 4, the memory demands by GCFP are significantly larger. Calculation of GCFPs of A=12 system at E=1 requires 145 MB. The program parGCFP requires additional 2.5 and 4.5 MB of memory for the serial and parallel version, respectively. Classification: 17.18 Nature of problem: The program GCFP generates a list of two-particle coefficients of fractional parentage for several j-shells with isospin. Solution method: The method is based on the observation that multishell coefficients of fractional parentage can be expressed in terms of single-shell CFPs [1]. The latter are calculated using the algorithm [2,3] for a spectral decomposition of an antisymmetrization operator matrix Y. The coefficients of fractional parentage are those eigenvectors of the antisymmetrization operator matrix Y that correspond to unit eigenvalues. A computer code for these coefficients is available [4]. The program GCFP offers computation of two-particle multishell coefficients of fractional parentage. The program parGCFP allows a batch calculation using one input file. Sets of GCFPs are independent and can be calculated in parallel. Restrictions:A<86 when E=0 (due to the memory constraints); small numbers of particles allow significantly higher excitations, though the shell with j⩾11/2 cannot get full (it is the implementation constraint). Unusual features: Using the program GCFP it is possible to determine allowed particle configurations without the GCFP computation. The GCFPs can be calculated either for all particle configurations at once or for a specified particle configuration. The values of GCFPs can be printed out with a complete specification in either one file or with the parent and daughter configurations printed in separate files. The latter output mode requires additional time and RAM memory. It is possible to restrict the ( J,T) values of the considered particle configurations. (Here J is the total angular momentum and T is the total isospin of the system.) The program parGCFP produces several result files the number of which equals to the number of particle configurations. To work correctly, the program GCFP needs to be compiled to read parameters from the standard input (the default setting). Running time: It depends on the size of the problem. The minimum time is required, if the computation and output mode ( CompMode) is not 4, but the resulting file is larger. A system with A=12 particles at E=0 (all 9411 GCFPs) took around 1 sec on a Pentium4 2.8 GHz processor with 1 MB L2 cache. The program required about 14 min to calculate all 1.3×10 GCFPs of E=1. The time for all 5.5×10 GCFPs of E=2 was about 53 hours. For this number of particles, the calculation time of both E=0 and E=1 with CompMode = 1 and 4 is nearly the same, when no other processes are running. The case of E=2 could not be calculated with CompMode = 4, because the RAM memory was insufficient. In general, the latter CompMode requires a longer computation time, although the resulting files are smaller in size. The program parGCFP puts virtually no time overhead. Its parallel version speeds-up the calculation. However, the results need to be collected from several files created for each configuration. References: [1] J. Levinsonas, Works of Lithuanian SSR Academy of Sciences 4 (1957) 17. [2] A. Deveikis, A. Bončkus, R. Kalinauskas, Lithuanian Phys. J. 41 (2001) 3. [3] A. Deveikis, R.K. Kalinauskas, B.R. Barrett, Ann. Phys. 296 (2002) 287. [4] A. Deveikis, Comput. Phys. Comm. 173 (2005) 186. (CPC Catalogue ID. ADWI_v1_0)
Generalized entering coefficients: A criterion for foam stability against oil in porous media
Bergeron, V.; Fagan, M.E.; Radke, C.J. Univ. of California, Berkeley, CA )
1993-07-01
The unique mobility-control properties of foam in porous media make it an attractive choice as an injection fluid for enhanced oil recovery. 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. 48 refs., 14 figs., 4 tabs.
Generalized entering coefficients: A criterion for foam stability against oil in porous media
Bergeron, V.; Fagan, M.E.; Radke, C.J.
1993-09-01
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.
A generalized entering coefficient to characterize foam stability against oil in porous media
Bergeron, V.; Fagan, M.E.; Radke, C.J.
1992-11-01
This work unifies the two approaches presently accounting for oil-foam interactions: spreading behavior and thin-film stability. We demonstrate the correspondences between stable pseudoemulsion films, negative entering coeffients, and oil-tolerant foams. Frumkin-Deryaguin theory is applied to the problem of oil-foam interactions and reveals that stable pseudoemulsion films are essential to maintain oil-tolerant foams. This hypothesis is critically tested by comparing steady-state foam flow behavior in glass beadpacks that contain residual oil, with newly measured, equilibrium disjoining pressure isotherms for both foam and pseudoemulsion films, along with bulk surface and interfacial tensions. Experimental results together with similar data on a wide variety of systems lead us to conclude that highly repulsive pseudoemulsion film disjoining pressure isotherms (i.e., stable pseudoemulsion films) produce negative generalized entering coefficients and oil-tolerant foams. This in turn provides us with a surfactant design criterion needed to produce oil-tolerant foam in porous media.
ERIC Educational Resources Information Center
Yan, Jun; Aseltine, Robert H., Jr.; Harel, Ofer
2013-01-01
Comparing regression coefficients between models when one model is nested within another is of great practical interest when two explanations of a given phenomenon are specified as linear models. The statistical problem is whether the coefficients associated with a given set of covariates change significantly when other covariates are added into…
ERIC Educational Resources Information Center
Yan, Jun; Aseltine, Robert H., Jr.; Harel, Ofer
2013-01-01
Comparing regression coefficients between models when one model is nested within another is of great practical interest when two explanations of a given phenomenon are specified as linear models. The statistical problem is whether the coefficients associated with a given set of covariates change significantly when other covariates are added into
Variable stiffness torsion springs
NASA Technical Reports Server (NTRS)
Alhorn, Dean C. (inventor); Polites, Michael E. (inventor)
1994-01-01
In a torsion spring the spring action is a result of the relationships between the torque applied in twisting the spring, the angle through which the torsion spring twists, and the modulus of elasticity of the spring material in shear. Torsion springs employed industrially have been strips, rods, or bars, generally termed shafts, capabable of being flexed by twisting their axes. They rely on the variations in shearing forces to furnish an internal restoring torque. In the torsion springs herein the restoring torque is external and therefore independent of the shearing modulus of elasticity of the torsion spring shaft. Also provided herein is a variable stiffness torsion spring. This torsion spring can be so adjusted as to have a given spring constant. Such variable stiffness torsion springs are extremely useful in gimballed payloads such as sensors, telescopes, and electronic devices on such platforms as a space shuttle or a space station.
Variable stiffness torsion springs
NASA Technical Reports Server (NTRS)
Alhorn, Dean C. (inventor); Polites, Michael E. (inventor)
1995-01-01
In a torsion spring the spring action is a result of the relationships between the torque applied in twisting the spring, the angle through which the torsion spring twists, and the modulus of elasticity of the spring material in shear. Torsion springs employed industrially have been strips, rods, or bars, generally termed shafts, capabable of being flexed by twisting their axes. They rely on the variations in shearing forces to furnish an internal restoring torque. In the torsion springs herein the restoring torque is external and therefore independent of the shearing modulus of elasticity of the torsion spring shaft. Also provided herein is a variable stiffness torsion spring. This torsion spring can be so adjusted as to have a given spring constant. Such variable stiffness torsion springs are extremely useful in gimballed payloads such as sensors, telescopes, and electronic devices on such platforms as a space shuttle or a space station.
Planeta, Josef; Karsek, Pavel; Hohnov, Barbora; S?avkov, Lenka; Roth, Michal
2012-08-10
Biphasic solvent systems composed of an ionic liquid (IL) and supercritical carbon dioxide (scCO(2)) have become frequented in synthesis, extractions and electrochemistry. In the design of related applications, information on interphase partitioning of the target organics is essential, and the infinite-dilution partition coefficients of the organic solutes in IL-scCO(2) systems can conveniently be obtained by supercritical fluid chromatography. The data base of experimental partition coefficients obtained previously in this laboratory has been employed to test a generalized predictive model for the solute partition coefficients. The model is an amended version of that described before by Hiraga et al. (J. Supercrit. Fluids, in press). Because of difficulty of the problem to be modeled, the model involves several different concepts - linear solvation energy relationships, density-dependent solvent power of scCO(2), regular solution theory, and the Flory-Huggins theory of athermal solutions. The model shows a moderate success in correlating the infinite-dilution solute partition coefficients (K-factors) in individual IL-scCO(2) systems at varying temperature and pressure. However, larger K-factor data sets involving multiple IL-scCO(2) systems appear to be beyond reach of the model, especially when the ILs involved pertain to different cation classes. PMID:22552202
NASA Astrophysics Data System (ADS)
Wang, Lu; Wu, Li-Wei; Wei, Le; Gao, Juan; Sun, Cui-Li; Chai, Pei; Li, Dao-Wu
2014-02-01
The accuracy of attenuation correction in positron emission tomography scanners depends mainly on deriving the reliable 511-keV linear attenuation coefficient distribution in the scanned objects. In the PET/CT system, the linear attenuation distribution is usually obtained from the intensities of the CT image. However, the intensities of the CT image relate to the attenuation of photons in an energy range of 40 keV-140 keV. Before implementing PET attenuation correction, the intensities of CT images must be transformed into the PET 511-keV linear attenuation coefficients. However, the CT scan parameters can affect the effective energy of CT X-ray photons and thus affect the intensities of the CT image. Therefore, for PET/CT attenuation correction, it is crucial to determine the conversion curve with a given set of CT scan parameters and convert the CT image into a PET linear attenuation coefficient distribution. A generalized method is proposed for converting a CT image into a PET linear attenuation coefficient distribution. Instead of some parameter-dependent phantom calibration experiments, the conversion curve is calculated directly by employing the consistency conditions to yield the most consistent attenuation map with the measured PET data. The method is evaluated with phantom experiments and small animal experiments. In phantom studies, the estimated conversion curve fits the true attenuation coefficients accurately, and accurate PET attenuation maps are obtained by the estimated conversion curves and provide nearly the same correction results as the true attenuation map. In small animal studies, a more complicated attenuation distribution of the mouse is obtained successfully to remove the attenuation artifact and improve the PET image contrast efficiently.
Dimitriadis, Alexandros I.; Kantartzis, Nikolaos V.; Tsiboukis, Theodoros D.; Hafner, Christian
2015-01-15
Highlights: •Formulas for E/M fields radiated by continuous surface polarization distributions. •Non-local effective surface susceptibility model for periodic metafilms. •Generalized reflection and transmission coefficients for an arbitrary metafilm. •Successful treatment of non-planar scatterer arrays and spatial dispersion effects. -- Abstract: A non-local surface susceptibility model for the consistent description of periodic metafilms formed by arbitrarily-shaped, electrically-small, bianisotropic scatterers is developed in this paper. The rigorous scheme is based on the point-dipole approximation technique and is valid for any polarization and propagation direction of an electromagnetic wave impinging upon the metafilm, unlike existing approaches whose applicability is practically confined to very specific cases of incidence. Next, the universal form of the resulting surface susceptibility matrix is employed for the derivation of the generalized Fresnel coefficients for such surfaces, which enable the comprehensive interpretation of several significant, yet relatively unexamined, physical interactions. Essentially, these coefficients include eight distinct terms, corresponding to the co-polarized and cross-polarized reflection and transmission coefficients for the two orthogonal eigenpolarizations of a linearly-polarized incident plane wave. The above formulas are, then, utilized for the prediction of the scattering properties of metafilms with different planar and non-planar resonators, which are characterized via the featured model and two previously reported local ones. Their comparison with numerical simulation outcomes substantiates the merits of the proposed method, reveals important aspects of the underlying physics, and highlights the differences between the various modeling procedures.
Generalized Skew Coefficients of Annual Peak Flows for Rural, Unregulated Streams in West Virginia
Atkins, John T.; Wiley, Jeffrey B.; Paybins, Katherine S.
2009-01-01
Generalized skew was determined from analysis of records from 147 streamflow-gaging stations in or near West Virginia. The analysis followed guidelines established by the Interagency Advisory Committee on Water Data described in Bulletin 17B, except that stations having 50 or more years of record were used instead of stations with the less restrictive recommendation of 25 or more years of record. The generalized-skew analysis included contouring, averaging, and regression of station skews. The best method was considered the one with the smallest mean square error (MSE). MSE is defined as the following quantity summed and divided by the number of peaks: the square of the difference of an individual logarithm (base 10) of peak flow less the mean of all individual logarithms of peak flow. Contouring of station skews was the best method for determining generalized skew for West Virginia, with a MSE of about 0.2174. This MSE is an improvement over the MSE of about 0.3025 for the national map presented in Bulletin 17B.
Chen, Yao; Ho, Daniel W C; Lu, Jinhu; Lin, Zongli
2016-01-01
Multiagent systems (MASs) are ubiquitous in our real world. There is an increasing attention focusing on the consensus (or synchronization) problem of MASs over the past decade. Although there are numerous results reported on the convergence of a discrete-time MAS based on the infinite products of matrices, few results are on the convergence rate. Because of the switching topology, the traditional eigenvalue analysis and the Lyapunov function methods are both invalid for the convergence rate analysis of an MAS with a switching topology. Therefore, the estimation of the convergence rate for a discrete-time MAS with time-varying delays remains a difficult problem. To overcome the essential difficulty of switching topology, this paper aims at developing a contractive-set approach to analyze the convergence rate of a discrete-time MAS in the presence of time-varying delays and generalized coupling coefficients. Using the proposed approach, we obtain an upper bound of the convergence rate under the condition of joint connectivity. In particular, the proposed method neither requires the nonnegative property of the coupling coefficients nor the basic assumption of a uniform lower bound for all positive coupling coefficients, which have been widely applied in the existing works on this topic. As an application of the main results, we will show that the classical Vicsek model with time delays can realize synchronization if the initial topology is connected. PMID:26357412
Lee, S H; Van der Werf, J H J
2006-10-01
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 genotypes for such a pedigree make it infeasible to estimate dominance relationship coefficients between individuals. In this study, identity-by-descent (IBD) coefficients are estimated on the basis of population-wide linkage disequilibrium (LD), which makes it possible to track dominance relationships between unrelated founders. Therefore, it is possible to use dominance effects in QTL mapping without full sibs. Incomplete genotypes with a complex pedigree and many markers can be efficiently dealt with by a Markov chain Monte Carlo method for estimating IBD and dominance relationship matrices (D(RM)). It is shown by simulation that the use of D(RM) increases the likelihood ratio at the true QTL position and the mapping accuracy and power with complete dominance, overdominance, and recessive inheritance modes when using 200 genotyped and phenotyped individuals. PMID:16951069
Orbai, Ana-Maria; Smith, Katherine C.; Bartlett, Susan J.; De Leon, Elaine; Bingham, Clifton O.
2014-01-01
Objective Stiffness is a well-recognized symptom of Rheumatoid Arthritis (RA). It is frequently queried during clinic visits as an indicator of disease activity, and was included in the 1961 and 1987 RA classification criteria. Little is known about how people with RA experience stiffness and its impact on their lives. Methods We conducted 4 focus groups with 20 people with RA (4-6 participants per group), from one academic clinical practice and one private practice, to generate accounts of stiffness experiences. Qualitative inductive thematic data analysis was conducted. Results Five overarching themes were identified: 1. Relationship of stiffness with other symptoms; 2. Exacerbating or alleviating factors and self-management; 3. Stiffness timing and location; 4. Individual meanings of stiffness experiences; 5. Impact of stiffness on daily life. Conclusion Focus group discussions revealed individual stiffness experiences as diverse and complex. Several stiffness features were endorsed by a majority of participants, but few, if any, were universally experienced, thus the significance of stiffness as an expression of the disease varied widely. Discussions yielded descriptions of how individual limits imposed by RA in general and stiffness in particular, may change over time and were intertwined with adaptations to preserve participation in valued life activities. These results concerning the diversity of the stiffness experience, consequential adaptations, and its impact suggest a more individualized approach to stiffness measurement may be needed in order to improve stiffness assessments. PMID:24891304
Characteristics of high-stiffness superconducting bearing
Okano, M.; Tamada, N.; Fuchino, S.; Ishii, I.
1996-07-01
Magnetic bearings using a high-Tc superconductor have been studied. Generally the bearing makes use of the pinning effects to get the levitation force. The stiffness of the bearing, however, is extremely low as compared with industrial-scale conventional one. To improve the bearing stiffness the authors propose a disc-type repulsive superconducting thrust bearing with a slit for the restraint of the flux. Both theoretical and experimental evaluation on the load performance was carried out, and it is clarified that the proposed superconducting bearing has higher stiffness.
Magnetic negative stiffness dampers
NASA Astrophysics Data System (ADS)
Shi, Xiang; Zhu, Songye
2015-07-01
This communication presents the design principle and experimental validation of two novel configurations of magnetic negative stiffness dampers (MNSDs), both of which are composed of several permanent magnets arranged in a conductive pipe. The MNSD, as a passive device, efficiently integrates negative stiffness and eddy-current damping in a simple and compact design, in which the negative stiffness behavior depends on the different arrangements of the permanent magnets. When applied to structural vibration control, passive MNSD may achieve a performance comparable with semi-active or active control in some applications. Laboratory experiments of small-scale prototypes successfully verified the proposed MNSD design concept.
NASA Technical Reports Server (NTRS)
Nelson, C. C.; Childs, D. W.; Nicks, C.; Elrod, D.
1985-01-01
The leakage and rotordynamic coefficients of constant-clearance and convergent-tapered annular gas seals were measured in an experimental test facility. The results are presented along with the theoretically predicted values. Of particular interest is the prediction that optimally tapered seals have significantly larger direct stiffness than straight seals. The experimental results verify this prediction. Generally the theory does quite well, but fails to predict the large increase in direct stiffness when the fluid is pre-rotated.
NASA Technical Reports Server (NTRS)
Coward, Adrian V.; Papageorgiou, Demetrios T.; Smyrlis, Yiorgos S.
1994-01-01
In this paper the nonlinear stability of two-phase core-annular flow in a pipe is examined when the acting pressure gradient is modulated by time harmonic oscillations and viscosity stratification and interfacial tension is present. An exact solution of the Navier-Stokes equations is used as the background state to develop an asymptotic theory valid for thin annular layers, which leads to a novel nonlinear evolution describing the spatio-temporal evolution of the interface. The evolution equation is an extension of the equation found for constant pressure gradients and generalizes the Kuramoto-Sivashinsky equation with dispersive effects found by Papageorgiou, Maldarelli & Rumschitzki, Phys. Fluids A 2(3), 1990, pp. 340-352, to a similar system with time periodic coefficients. The distinct regimes of slow and moderate flow are considered and the corresponding evolution is derived. Certain solutions are described analytically in the neighborhood of the first bifurcation point by use of multiple scales asymptotics. Extensive numerical experiments, using dynamical systems ideas, are carried out in order to evaluate the effect of the oscillatory pressure gradient on the solutions in the presence of a constant pressure gradient.
NASA Astrophysics Data System (ADS)
Shen, Yu-Jia; Gao, Yi-Tian; Yu, Xin
2013-09-01
With symbolic computation, the generalized variable-coefficient Drinfeld-Sokolov-Satsuma-Hirota (gvcDSSH) system in fluids and plasmas is investigated. Under the constraint conditions on variable coefficients obtained via the Painlev test, the binary Bell polynomials are applied to the gvcDSSH system for its bilinear forms and multi-soliton solutions. With the different damping, dispersive and dissipative coefficients given, the multi-soliton solutions of the gvcDSSH system are illustrated and discussed. (i) The interactions between/among the solitons are elastic; (ii) the damping coefficient can only affect the amplitude of one field, while it has no effect on the other; (iii) the velocity and characteristic line for each soliton can be affected by the dispersive and dissipative coefficients.
Nandi, Sumon; Maschke, Steven; Evans, Peter J; Lawton, Jeffrey N
2009-12-01
Elbow motion is essential for upper extremity function to position the hand in space. Unfortunately, the elbow joint is prone to stiffness following a multitude of traumatic and atraumatic etiologies. Elbow stiffness can be diagnosed with a complete history and physical exam, supplemented with appropriate imaging studies. The stiff elbow is challenging to treat, and thus, its prevention is of paramount importance. When this approach fails, non-operative followed by operative treatment modalities should be pursued. Upon initial presentation in those who have minimal contractures of 6-month duration or less, static and dynamic splinting, serial casting, continuous passive motion, occupational/physical therapy, and manipulation are non-operative treatment modalities that may be attempted. A stiff elbow that is refractory to non-operative management can be treated surgically, either arthroscopically or open, to eliminate soft tissue or bony blocks to motion. In the future, efforts to prevent and treat elbow stiffness may target the basic science mechanisms involved. Our purpose was to review the etiologies, classification, evaluation, prevention, operative, and non-operative treatment of the stiff elbow. PMID:19350328
Gopinathan, K.K. )
1988-01-01
Correlations are developed to estimate the regression coefficients a and b of {Angstrom} type correlations for predicting monthly mean daily global solar radiation on a horizontal surface. The suggested equations express the regression coefficients in terms of the latitude, elevation, and percent of possible sunshine and are applicable to any location around the world to compute global solar radiation on horizontal surfaces.
Optimized stiffness for linear time-invariant dynamic system according to a new system design
NASA Astrophysics Data System (ADS)
Veeraklaew, Tawiwat
2012-11-01
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.
Lumia, Richard; Baevsky, Yvonne Halpern
2000-01-01
Flood-frequency relations that are developed by fitting the logarithms of annual peak discharges to a Pearson Type-III distribution are sensitive to skew coefficients. Estimates of population skew for a site are improved when computed from the weighted average of (1) the sample (station) skew, and (2) an unbiased, generalized skew estimate. A weighting technique based on the number of years of record at each of 226 sites was used to develop a contour map of unbiased, generalized skew coefficients for New York. An attempt was made to group (regionalize) the station skew coefficients into five hydrologically similar areas of New York, but the statewide version proved to be as accurate as the regionalized version and therefore was adopted as the final generalized skew-coefficient map for New York. An error analysis showed the statewide contour map to have lower MSE?s (mean square errors) than those computed from (1) the five regional skewcoefficient contour maps, (2) a previously used (1982) nationwide skew coefficient map, and (3) the weighted mean of skew coefficients for sites within each of five hydrologically uniform, but distinct areas of New York.
Reflectional transformation for structural stiffness
Vashi, K.M.
1990-01-01
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.
Stiff-system problems and solutions at LLNL
Hindmarsh, A.C.
1982-03-01
Difficult stiff system problems encountered at LLNL are typified by those arising from various atmospheric kinetics models, which include reaction kinetics and transport in up to two space dimensions. Approaches devised for these problems resulted in several general purpose stiff system solvers. These have since evolved into a new systematized collection of solvers, called ODEPACK, based on backward differentiation formulas in the stiff case. A model kinetics-transport problem is used to illustrate the various solvers.
Pulling a polymer with anisotropic stiffness near a sticky wall
NASA Astrophysics Data System (ADS)
Tabbara, R.; Owczarek, A. L.
2012-11-01
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 models physical variablesnamely, 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.
NASA Astrophysics Data System (ADS)
Sibgatullin, K. E.; Sibgatullin, E. S.
2014-12-01
The bars of any form made of a uniform anisotropic material are considered. Generally in the cross section of a bar all internal power factors (IPF) - three forces and three moments are other than zero. Values IPF are known from the solution of the corresponding task. The coefficient of a stock of bearing ability of a bar is defined by a way of comparison of known vector IPF vec R* with the corresponding required vector of durability vec R in IPF space.
Lue Xing Zhu Hongwu; Yao Zhenzhi; Meng Xianghua; Zhang Cheng; Zhang Chunyi; Tian Bo
2008-08-15
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.
Horváth, Tamás; Osztovits, János; Pintér, Alexandra; Littvay, Levente; Cseh, Domonkos; Tárnoki, Adám D; Tárnoki, Dávid L; Jermendy, Adám L; Steinbach, Rita; Métneki, Júlia; Schillaci, Giuseppe; Kollai, Márk; Jermendy, György
2014-01-01
Arterial stiffness is an independent predictor of cardiovascular, cerebrovascular and all-cause mortality. Quantifying the genetic influence on the stiff arterial phenotype allows us to better predict the development of arterial stiffness. In this study, we aimed to determine the heritability of carotid artery stiffness in healthy twins. We studied 98 twin pairs of both sexes. We determined carotid artery stiffness locally using echo tracking and applanation tonometry. We estimated the heritability of stiffness parameters using structural equation modeling. The carotid distensibility coefficient showed the highest heritability (64%, 95% confidence interval 45-77%). The incremental elastic modulus, compliance and stiffness index β also showed substantial heritability (62%, 61% and 58%, respectively). The remaining 36-42% phenotypic variance was attributed to unshared environmental effects. Genetic influence appears to dominate over environmental factors in the development of carotid artery stiffness. Environmental factors may have an important role in favorably influencing the genetic predisposition for accelerated arterial stiffening. PMID:24089266
NASA Astrophysics Data System (ADS)
Baskakov, A. P.; Rakov, O. A.
2013-11-01
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.).
NASA Technical Reports Server (NTRS)
Majda, G.
1985-01-01
A large set of variable coefficient linear systems of ordinary differential equations which possess two different time scales, a slow one and a fast one is considered. A small parameter epsilon characterizes the stiffness of these systems. A system of o.d.e.s. in this set is approximated by a general class of multistep discretizations which includes both one-leg and linear multistep methods. Sufficient conditions are determined under which each solution of a multistep method is uniformly bounded, with a bound which is independent of the stiffness of the system of o.d.e.s., when the step size resolves the slow time scale, but not the fast one. This property is called stability with large step sizes. The theory presented lets one compare properties of one-leg methods and linear multistep methods when they approximate variable coefficient systems of stiff o.d.e.s. In particular, it is shown that one-leg methods have better stability properties with large step sizes than their linear multistep counter parts. The theory also allows one to relate the concept of D-stability to the usual notions of stability and stability domains and to the propagation of errors for multistep methods which use large step sizes.
Dynamically variable negative stiffness structures.
Churchill, Christopher B; Shahan, David W; Smith, Sloan P; Keefe, Andrew C; McKnight, Geoffrey P
2016-02-01
Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness-based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators. PMID:26989771
Stiffnesses of laminated flat plates
NASA Astrophysics Data System (ADS)
1994-04-01
ESDU 94003 gives formulae for the in-plane and flexural stiffnesses of laminated flat plates built-up from thin orthotropic layers that may have different material properties, thicknesses, and orientations of their principal axes of orthotropy. The influence of the lay-up arrangement on the plate stiffnesses is explained. A complete list of possible forms of the stiffness matrices is provided with in each case examples of possible lay-up arrangements that will give them. Although it is normally convenient to use the central plane of the plate as the reference plane, subsequent calculations may be simplified by adopting another parallel reference plane; formulae are given for the values of the coupled in-plane and flexural stiffness matrix and the flexural stiffness matrix of the plate for such a shift of reference plane. The in-plane stiffness matrix is unaffected. A worked example illustrates the calculation of the stiffnesses. The relationship between the stiffnesses of a layer and the complete matrix of the elastic constants for an anisotropic solid is included. The relationship of the stiffnesses of both isotropic plates and sandwich panels with the laminated plate stiffnesses is also given. Equations are given relating the stress and strain in a layer in one axis system to those in another. The formulae apply to composite plates with systematic fibrous reinforcements in metallic or non-metallic matrices.
NASA Astrophysics Data System (ADS)
Yuan, Du-Qi; Wang, Can-Jun
2010-04-01
Based on the form of the n-dimensional generic power-law potential, the state equation and the heat capacity, the analytical expressions of the Joule-Thomson coefficient (JTC) for an ideal Bose gas are derived in n-dimensional potential. The effect of the spatial dimension and the external potential on the JTC are discussed, respectively. These results show that: (i) For the free ideal Bose gas, when n/s <= 2 (n is the spatial dimension, s is the momentum index in the relation between the energy and the momentum), and T ? TC (TC is the critical temperature), the JTC can obviously improve by means of changing the throttle valve's shape and decreasing the spatial dimension of gases. (ii) For the inhomogeneous external potential, the discriminant ? = [1 - ?[ni = 1(kT/varpii)1/ti?(1/ti + 1)] (k is the Boltzmann Constant, T is the thermodynamic temperature, varpii is the external field's energy), is obtained. The potential makes the JTC increase when ? > 0, on the contrary, it makes the JTC decrease when ? < 0. (iii) In the homogenous strong external potential, the JTC gets the maximum on the condition of kT/varpii < 1.
NASA Astrophysics Data System (ADS)
Basarab-Horwath, P.; Gngr, F.; zemir, C.
2013-11-01
We consider generalized KP-Burgers equations and attempt to identify subclasses admitting Virasoro or Kac-Moody type algebras as their symmetries. We give reductions to ODEs constructed from invariance requirement under these infinite-dimensional Lie symmetry algebras and integrate them in cases where it is possible. We also look at the conditions under which the equation passes the Painlev test and construct some exact solutions by truncation.
Dynamically variable negative stiffness structures
Churchill, Christopher B.; Shahan, David W.; Smith, Sloan P.; Keefe, Andrew C.; McKnight, Geoffrey P.
2016-01-01
Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness–based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators. PMID:26989771
Dynamic dorsoventral stiffness assessment of the ovine lumbar spine.
Keller, Tony S; Colloca, Christopher J
2007-01-01
Posteroanterior spinal stiffness assessments are common in the evaluating patients with low back pain. The purpose of this study was to determine the effects of mechanical excitation frequency on dynamic lumbar spine stiffness. A computer-controlled voice coil actuator equipped with a load cell and LVDT was used to deliver an oscillatory dorsoventral (DV) mechanical force to the L3 spinous process of 15 adolescent Merino sheep. DV forces (48 N peak, approximately 10% body weight) were randomly applied at periodic excitation frequencies of 2.0, 6.0, 11.7 and a 0.5-19.7 Hz sweep. Force and displacement were recorded over a 13-22 s time interval. The in vivo DV stiffness of the ovine spine was frequency dependent and varied 3.7-fold over the 0.5-19.7 Hz mechanical excitation frequency range. Minimum and maximum DV stiffness (force/displacement) were 3.86+/-0.38 and 14.1+/-9.95 N/mm at 4.0 and 19.7 Hz, respectively. Stiffness values based on the swept-sine measurements were not significantly different from corresponding periodic oscillations (2.0 and 6.0 Hz). The mean coefficient of variation in the swept-sine DV dynamic stiffness assessment method was 15%, which was similar to the periodic oscillation method (10-16%). The results indicate that changes in mechanical excitation frequency and animal body mass modulate DV spinal stiffness. PMID:16376350
Rea, A.H.; Tortorelli, R.L.
1997-01-01
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.
NASA Astrophysics Data System (ADS)
Yuping, Zhang; Junyi, Wang; Guangmei, Wei; Ruiping, Liu
2015-06-01
A generalized variable-coefficient Korteweg-de Vries (KdV) equation with variable-coefficients of x and t from fluids and plasmas is investigated in this paper. The explicit Painlev-integrable conditions are given out by Painlev test, and an auto-Bcklund transformation is presented via the truncated Painlev expansion. Under the integrable condition and auto-Bcklund transformation, the analytic solutions are provided, including the soliton-like, periodic and rational solutions. Lax pair, Riccati-type auto-Bcklund transformation (R-BT) and Wahlquist-Estabrook-type auto-Bcklund transformation (WE-BT) are constructed in extended AKNS system. One-soliton-like and two-soliton-like solutions are obtained by R-BT and nonlinear superposition formula is obtained by WE-BT. The bilinear form and N-soliton-like solutions are presented by Bell-polynomial approach. Based on the obtained analytic solutions, the propagation characteristics of waves effected by the variable coefficients are discussed.
NASA Astrophysics Data System (ADS)
Gao, Xin-Yi
2015-04-01
Plasmas are known as the most abundant form of matter in the Universe. Nowadays, with respect to the cosmic plasmas, considerable efforts have been put into investigating the experimentally relevant Korteweg-de Vries (KdV)-Burgers-type equations. In this letter, with plenty of experimental/observational support presented, symbolic computation on a general variable-coefficient KdV-Burgers equation is performed, which covers the models for a variety of the cosmic plasmas. An auto-Bcklund transformation is constructed out, along with two families of the analytic solitonic solutions, for the electrostatic wave potential, perturbation of the magnitude of the magnetic field, fluctuation of electron or ion density, or radial-direction component of the velocity of ions or dust particles. Both our auto-Bcklund transformation and solitonic solutions depend on the cosmic-plasma parameters by way of the nonlinearity, dispersion, dissipation and geometric-effect coefficient functions, as to the ion-acoustic, magnetoacoustic, electron-acoustic, positron-acoustic, dust-acoustic and quantum dust-ion-acoustic waves. The shock structures from our analytic investigation agree well with to those experimentally reported. Certain effects of a cosmic-plasma system, described by such variable coefficients, might be detected by the future plasma experiments/observations.
Dynamic stiffness removal for direct numerical simulations
Lu, Tianfeng; Law, Chung K.; Yoo, Chun Sang; Chen, Jacqueline H.
2009-08-15
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)
Reliability of Unilateral Vertical Leg Stiffness Measures Assessed During Bilateral Hopping.
Maloney, Sean J; Fletcher, Iain M; Richards, Joanna
2015-10-01
The assessment of vertical leg stiffness is an important consideration given its relationship to performance. Vertical stiffness is most commonly assessed during a bilateral hopping task. The current study sought to determine the intersession reliability, quantified by the coefficient of variation, of vertical stiffness during bilateral hopping when assessed for the left and right limbs independently, which had not been previously investigated. On 4 separate occasions, 10 healthy males performed 30 unshod bilateral hops on a dual force plate system with data recorded independently for the left and right limbs. Vertical stiffness was calculated as the ratio of peak ground reaction force to the peak negative displacement of the center of mass during each hop and was averaged over the sixth through tenth hops. For vertical stiffness, average coefficients of variation of 15.3% and 14.3% were observed for the left and right limbs, respectively. An average coefficient of variation of 14.7% was observed for bilateral vertical stiffness. The current study reports that calculations of unilateral vertical stiffness demonstrate reliability comparable to bilateral calculations. Determining unilateral vertical stiffness values and relative discrepancies may allow a coach to build a more complete stiffness profile of an individual athlete and better inform the training process. PMID:25880542
NASA Astrophysics Data System (ADS)
Collier, Craig S.
1993-04-01
A method is presented for formulating stiffness terms and thermal coefficients of stiffened, fiber-reinforced composite panels. The method is robust enough to handle panels with general cross sectional shapes, including those which are unsymmetric and/or unbalanced. Nonlinear, temperature and load dependent constitutive material data of each laminate are used to 'build-up' the stiffened panel membrane, bending, and membrane-bending coupling stiffness terms and thermal coefficients. New thermal coefficients are introduced to quantify panel response from through-the-thickness temperature gradients. A technique of implementing this capability with a single plane of shell finite elements using the MSC/NASTRAN analysis program (FEA) is revealed that provides accurate solutions of entire airframes or engines with coarsely meshed models. An example of a composite, hat-stiffened panel is included to demonstrate errors that occur when an unsymmetric panel is symmetrically formulated as traditionally done. The erroneous results and the correct ones produced from this method are compared to analysis from discretely meshed three-dimensional FEA.
NASA Technical Reports Server (NTRS)
Collier, Craig S.
1993-01-01
A method is presented for formulating stiffness terms and thermal coefficients of stiffened, fiber-reinforced composite panels. The method is robust enough to handle panels with general cross sectional shapes, including those which are unsymmetric and/or unbalanced. Nonlinear, temperature and load dependent constitutive material data of each laminate are used to 'build-up' the stiffened panel membrane, bending, and membrane-bending coupling stiffness terms and thermal coefficients. New thermal coefficients are introduced to quantify panel response from through-the-thickness temperature gradients. A technique of implementing this capability with a single plane of shell finite elements using the MSC/NASTRAN analysis program (FEA) is revealed that provides accurate solutions of entire airframes or engines with coarsely meshed models. An example of a composite, hat-stiffened panel is included to demonstrate errors that occur when an unsymmetric panel is symmetrically formulated as traditionally done. The erroneous results and the correct ones produced from this method are compared to analysis from discretely meshed three-dimensional FEA.
Chotel, Franck; Braillon, Pierre; Sailhan, Frdric; Gadeyne, Sylvain; Panczer, Grard; Pedrini, Christian; Berard, Jrme
2008-01-01
Although there are many publications concerning the mechanical behavior of adult bone, there are few data about mechanical properties of children's bone. In vivo bone stiffness measurement with Orthometer device has been validated and extensively used in adults to assess bone healing after fracture or lengthening. We hypothesized that in vivo stiffness measurement with Orthometer was applicable in children and was correlated with age, height, body weight, and corpulence index. The purpose was to establish baseline stiffness values for femur and tibia in growing children.Sixteen bone measurements (7 femurs and 9 tibias) were obtained during application of an external fixator for leg lengthening in 11 children aged between 5.5 and 16.7 years. A 3-point bending test with an Orthometer was carried out on the intact bone (before osteotomy) under general anesthesia. The anteroposterior stiffness measurement was successful in all children of the series, aged from 5.5 to 16.7 years. A wide variation of femoral and tibial bone stiffness values were observed. The use of a unique value as in adults as the end point of bending stiffness during bone healing process is not possible for children. The anteroposterior bone stiffness was found to have linear correlation with children's height and body weight, but not with age and corpulence indexes. The original data obtained by this study will give a stiffness reference for height and weight and could be useful as reference values for monitoring of healing process after fracture or limb lengthening. PMID:18580368
Implicit Extrapolation Methods for Variable Coefficient Problems
NASA Technical Reports Server (NTRS)
Jung, M.; Ruede, U.
1996-01-01
Implicit extrapolation methods for the solution of partial differential equations are based on applying the extrapolation principle indirectly. Multigrid tau-extrapolation is a special case of this idea. In the context of multilevel finite element methods, an algorithm of this type can be used to raise the approximation order, even when the meshes are nonuniform or locally refined. Here previous results are generalized to the variable coefficient case and thus become applicable for nonlinear problems. The implicit extrapolation multigrid algorithm converges to the solution of a higher order finite element system. This is obtained without explicitly constructing higher order stiffness matrices but by applying extrapolation in a natural form within the algorithm. The algorithm requires only a small change of a basic low order multigrid method.
Quantitative evaluation of stiffness of commercial suture materials.
Chu, C C; Kizil, Z
1989-03-01
The bending stiffness of 22 commercial suture materials of varying size, chemical structure and physical form was quantitatively evaluated using a stiffness tester (Taber V-5, model 150B, Teledyne). The commercial sutures were Chromic catgut; Dexon (polyglycolic acid); Vicryl (polyglactin 910); PDS (polydioxanone); Maxon (polyglycolide-trimethylene carbonate); Silk (coated with silicone); Mersilene (polyester fiber); Tycron (polyester fiber); Ethibond (polyethylene terephthalate coated with polybutylene); Nurolon (nylon 66); Surgilon (nylon 66 coated with silicone); Ethilon (coated nylon 66), Prolene (polypropylene); Dermalene (polyethylene), and Gore-tex (polytetraflouroethylene). These are both natural and synthetic, absorbable and nonabsorbable and monofilament and multifilament sutures. All of these sutures were size 2-0, but Prolene sutures with sizes ranging from 1-0 to 9-0 were also tested to determine the effect of suture size on stiffness. The bending stiffness data obtained showed that a wide range of bending stiffness was observed among the 22 commercial sutures. The most flexible 2-0 suture was Gore-tex, followed by Dexon, Silk, Surgilon, Vicryl (uncoated), Tycron, Nurolon, Mersilene, Ethibond, Maxon, PDS, Ethilon, Prolene, Chromic catgut, coated Vicryl, and lastly, Dermalene. The large porous volume inherent in Gore-tex monofilament suture was the reason for its lowest flexural stiffness. Sutures with a braided structure were generally more flexible than those of a monofilament structure, irrespective of the chemical constituents. Coated sutures had significantly higher stiffness than the corresponding uncoated ones. This is particularly true when polymers rather than wax were used as the coating material. This increase in stiffness is attributable to the loss of mobility under bending force in the fibers and yarns that make up the sutures. An increase in the size of the suture significantly increased the stiffness, and the magnitude of increase depended on the chemical constituent of the suture. The flexural stiffness of sutures was also found to depend on the duration of bending in the test for stiffness. In general, monofilament sutures exhibited the largest time-dependent stiffness. This was most pronounced with the Gore-tex suture. Most braided sutures also showed less time-dependence in stiffness. Nylon sutures did not exhibit this time-dependent phenomenon regardless of physical form. PMID:2919353
NASA Astrophysics Data System (ADS)
Rokhlin, S. I.; Wang, L.
2002-09-01
An efficient recursive algorithm, the stiffness matrix method, has been developed for wave propagation in multilayered generally anisotropic media. This algorithm has the computational efficiency and simplicity of the standard transfer matrix method and is unconditionally computationally stable for high frequency and layer thickness. In this algorithm, the stiffness (compliance) matrix is calculated for each layer and recursively applied to generate a stiffness (compliance) matrix for a layered system. Next, reflection and transmission coefficients are calculated for layered media bounded by liquid or solid semispaces. The results show that the method is stable for arbitrary number and thickness of layers and the computation time is proportional to the number of layers. It is shown both numerically and analytically that for a thick structure the solution approaches the solution for a semispace. This algorithm is easily adaptable to laminates with periodicity, such as multiangle lay-up composites. The repetition and symmetry of the unit cell are naturally incorporated in the recursive scheme. As an example the angle beam time domain pulse reflections from fluid-loaded multilayered composites have been computed and compared with experiment. Based on this method, characteristic equations for Lamb waves and Floquet waves in periodic media have also been determined. copyright 2002 Acoustical Society of America.
Lue Xing; Li Juan; Zhang Haiqiang; Xu Tao; Li Lili; Tian Bo
2010-04-15
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.
Terrace Width Distributions for Steps of Alternating Stiffness
NASA Astrophysics Data System (ADS)
Yancey, Jeremy; Richards, Howard L.
2003-03-01
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.
Fluid damping and fluid stiffness of tube arrays in crossflow
Chen, S.S.; Zhu, S.; Jendrzejczyk, J.A.
1994-06-01
Motion-dependent fluid forces acting on a tube array were measured as a function of excitation frequency, excitation amplitude, and flow velocity. Fluid-damping and fluid-stiffness coefficients were obtained from measured motion-dependent fluid forces as a function of reduced flow velocity and excitation amplitude. The water channel and test setup provide a sound facility for obtaining key coefficients for fluidelastic instability of tube arrays in crossflow. Once the motion-dependent fluid-force coefficients have been measured, a reliable design guideline, based on the unsteady flow theory, can be developed for fluidelastic instability of tube arrays in crossflow.
Time simulation of flutter with large stiffness changes
NASA Technical Reports Server (NTRS)
Karpel, Mordechay; Wieseman, Carol D.
1992-01-01
Time simulation of flutter, involving large local structural changes, is formulated with a state-space model that is based on a relatively small number of generalized coordinates. Free-free vibration modes are first calculated for a nominal finite-element model with relatively large fictitious masses located at the area of structural changes. A low-frequency subset of these modes is then transformed into a set of structural modal coordinates with which the entire simulation is performed. These generalized coordinates and the associated oscillatory aerodynamic force coefficient matrices are used to construct an efficient time-domain, state-space model for a basic aeroelastic case. The time simulation can then be performed by simply changing the mass, stiffness, and damping coupling terms when structural changes occur. It is shown that the size of the aeroelastic model required for time simulation with large structural changes at a few apriori known locations is similar to that required for direct analysis of a single structural case. The method is applied to the simulation of an aeroelastic wind-tunnel model. The diverging oscillations are followed by the activation of a tip-ballast decoupling mechanism that stabilizes the system but may cause significant transient overshoots.
Kengne, E.; Lakhssassi, A.; Vaillancourt, R.; Liu, Wu-Ming
2012-12-15
We present a double-mapping method (D-MM), a natural combination of a similarity with F-expansion methods, for obtaining general solvable nonlinear evolution equations. We focus on variable-coefficients complex Ginzburg-Landau equations (VCCGLE) with multi-body interactions. We show that it is easy by this method to find a large class of exact solutions of Gross-Pitaevskii and Gross-Pitaevskii-Ginzburg equations. We apply the D-MM to investigate the dynamics of Bose-Einstein condensation with two- and three-body interactions. As a surprising result, we obtained that it is very easy to use the built D-MM to obtain a large class of exact solutions of VCCGLE with two-body interactions via a generalized VCCGLE with two- and three-body interactions containing cubic-derivative terms. The results show that the proposed method is direct, concise, elementary, and effective, and can be a very effective and powerful mathematical tool for solving many other nonlinear evolution equations in physics.
Stiffness and damping of elastomeric O-ring bearing mounts
NASA Technical Reports Server (NTRS)
Smalley, A. J.
1977-01-01
A test rig to measure the dynamic stiffness and damping of elastomer O rings was described. Test results for stiffness and loss coefficient in the frequency range from 50 Hz to 1000 Hz are presented. Results are given for three different materials, for five temperatures, for three amplitudes, for five values of squeeze for three values of stretch for three values of cross-section diameter and for three values of groove width. All test data points were plotted. In addition, trend summary plots were presented which compare the effect of material, temperature, amplitude, squeeze, stretch, cross-section diameter, and groove width. O ring deflections under a static load for different material were presented; and effective static stiffness values were compared with dynamic values.
ARTHROSCOPIC TREATMENT OF ELBOW STIFFNESS
Vieira, Luis Alfredo Gómez; Dal Molin, Fabio Farina; Visco, Adalberto; Fernandes, Luis Filipe Daneu; dos Santos, Murilo Cunha Rafael; Cardozo Filho, Nivaldo Souza; Gómez Cordero, Nicolas Gerardo
2015-01-01
To present the arthroscopic surgical technique and the evaluation of the results from this technique for treating elbow stiffness. Methods: Between April 2007 and January 2010, ten elbows of ten patients with elbow stiffness underwent arthroscopic treatment to release the range of motion. The minimum follow-up was 11 months, with an average of 27 months. All the patients were male and their average age was 32.8 years (ranging from 22 to 48 years). After the arthroscopic treatment, they were followed up weekly in the first month and every three months thereafter. The clinical evaluation was made using the criteria of the University of California at Los Angeles (UCLA). Results: All the patients were satisfied with the results from the arthroscopic treatment. The average UCLA score was 33.8 points. Conclusion: Arthroscopic treatment for elbow stiffness is a minimally invasive surgical technique that was shown to be efficient for treating this complication.
Lase Ultrasonic Web Stiffness tester
Tim Patterson, Ph.D., IPST at Ga Tech
2009-01-12
The objective is to provide a sensor that uses non-contact, laser ultrasonics to measure the stiffness of paper during the manufacturing process. This will allow the manufacturer to adjust the production process in real time, increase filler content, modify fiber refining and as result produce a quality product using less energy. The sensor operates by moving back and forth across the paper web, at pre-selected locations firing a laser at the sheet, measuring the out-of-plane velocity of the sheet then using that measurement to calculate sheet stiffness.
Nonlinear Dynamics of Stiff Polymers
NASA Astrophysics Data System (ADS)
Goldstein, Raymond E.; Langer, Stephen A.
1995-08-01
A formalism is presented for the nonlinear dynamics of inextensible stiff polymers within the model of local viscous dissipation. By casting the internal elastic forces in an intrinsic representation, enforcing the constraint of local inextensibility through a Lagrange multiplier function, and utilizing techniques from the differential geometry of curve motion, the dynamics of configurations of arbitrary complexity is reduced to a scalar partial differential equation amenable to analytical and efficient numerical study. As an example, the formalism is applied to the ``folding'' dynamics of stiff polymers with pairwise self-interactions and intrinsic curvature.
Elnaggar, Sameh Y; Tervo, Richard; Mattar, Saba M
2014-05-01
A cavity (CV) with a dielectric resonator (DR) insert forms an excellent probe for the use in electron paramagnetic resonance (EPR) spectrometers. The probe's coupling coefficient, ?, the quality factor, Q, and the filling factor, ? are vital in assessing the EPR spectrometer's performance. Coupled mode theory (CMT) is used to derive general expressions for these parameters. For large permittivity the dominating factor in ? is the ratio of the DR and CV cross sectional areas rather than the dielectric constant. Thus in some cases, resonators with low dielectric constant can couple much stronger with the cavity than do resonators with a high dielectric constant. When the DR and CV frequencies are degenerate, the coupled ? is the average of the two uncoupled ones. In practical EPR probes the coupled ? is approximately half of that of the DR. The Q of the coupled system generally depends on the eigenvectors, uncoupled frequencies (?1,?2) and the individual quality factors (Q1,Q2). It is calculated for different probe configurations and found to agree with the corresponding HFSS simulations. Provided there is a large difference between the Q1, Q2 pair and the frequencies of DR and CV are degenerate, Q is approximately equal to double the minimum of Q1 and Q2. In general, the signal enhancement ratio, Iwithinsert/Iempty, is obtained from Q and ?. For low loss DRs it only depends on ?1/?2. However, when the DR has a low Q, the uncoupled Qs are also needed. In EPR spectroscopy it is desirable to excite only a single mode. The separation between the modes, ?, is calculated as a function of ? and Q. It is found to be significantly greater than five times the average bandwidth. Thus for practical probes, it is possible to excite one of the coupled modes without exciting the other. The CMT expressions derived in this article are quite general and are in excellent agreement with the lumped circuit approach and finite numerical simulations. Hence they can also be applied to a loop-gap resonator in a cavity. For the design effective EPR probes, one needs to consider the ?, Q and ? parameters. PMID:24607823
NASA Technical Reports Server (NTRS)
Nelson, C. C.; Childs, D. W.; Nicks, C.; Elrod, D.
1985-01-01
The leakage and rotordynamic coefficients of constant-clearance and convergent-tapered annular gas seals were measured in an experimental test facility. The results are presented along with the theoretically predicted values. Of particular interest is the prediction that optimally tapered seals have significantly larger direct siffness than straight seals. The experimental results verify this prediction. Generally the theory does quite well, but fails to predict the large increase in direct stiffness when the fluid is pre-rotated.
Cosmology with a stiff matter era
NASA Astrophysics Data System (ADS)
Chavanis, Pierre-Henri
2015-11-01
We consider the possibility that the Universe is made of a dark fluid described by a quadratic equation of state P =K ρ2 , where ρ is the rest-mass density and K is a constant. The energy density ɛ =ρ c2+K ρ2 is the sum of two terms: a rest-mass term ρ c2 that mimics "dark matter" (P =0 ) and an internal energy term u =K ρ2=P that mimics a "stiff fluid" (P =ɛ ) in which the speed of sound is equal to the speed of light. In the early universe, the internal energy dominates and the dark fluid behaves as a stiff fluid (P ˜ɛ , ɛ ∝a-6). In the late universe, the rest-mass energy dominates and the dark fluid behaves as pressureless dark matter (P ≃0 , ɛ ∝a-3). We provide a simple analytical solution of the Friedmann equations for a universe undergoing a stiff matter era, a dark matter era, and a dark energy era due to the cosmological constant. This analytical solution generalizes the Einstein-de Sitter solution describing the dark matter era, and the Λ CDM model describing the dark matter era and the dark energy era. Historically, the possibility of a primordial stiff matter era first appeared in the cosmological model of Zel'dovich where the primordial universe is assumed to be made of a cold gas of baryons. A primordial stiff matter era also occurs in recent cosmological models where dark matter is made of relativistic self-gravitating Bose-Einstein condensates (BECs). When the internal energy of the dark fluid mimicking stiff matter is positive, the primordial universe is singular like in the standard big bang theory. It expands from an initial state with a vanishing scale factor and an infinite density. We consider the possibility that the internal energy of the dark fluid is negative (while, of course, its total energy density is positive), so that it mimics anti-stiff matter. This happens, for example, when the BECs have an attractive self-interaction with a negative scattering length. In that case, the primordial universe is nonsingular and bouncing like in loop quantum cosmology. At t =0 , the scale factor is finite and the energy density is equal to zero. The universe first has a phantom behavior where the energy density increases with the scale factor, then a normal behavior where the energy density decreases with the scale factor. For the sake of generality, we consider a cosmological constant of arbitrary sign. When the cosmological constant is positive, the Universe asymptotically reaches a de Sitter regime where the scale factor increases exponentially rapidly with time. This can account for the accelerating expansion of the Universe that we observe at present. When the cosmological constant is negative (anti-de Sitter), the evolution of the Universe is cyclic. Therefore, depending on the sign of the internal energy of the dark fluid and on the sign of the cosmological constant, we obtain analytical solutions of the Friedmann equations describing singular and nonsingular expanding, bouncing, or cyclic universes.
Modulation of ankle stiffness during postural sway.
Lang, Christopher B; Kearney, Robert E
2014-01-01
Ankle stiffness is a nonlinear, time-varying system which contributes to the control of human upright stance. This study sought to examine the nature of the contribution of stiffness to postural control by determining how intrinsic and reflex stiffnesses varied with sway. Subjects were instructed to stand quietly on a bilateral electro-hydraulic actuator while perturbations were applied about the ankle. Subjects performed three types of trials: normal stance, forward lean, and backward lean. Position, torque, and EMGs from the tibialis anterior and triceps surae were recorded. Background torque, intrinsic stiffness and reflex stiffness were calculated for each perturbation. Intrinsic and reflex stiffnesses were heavily modulated by postural sway. Moreover, they were modulated in a complimentary manner; intrinsic stiffness was lowest when reflex gain was highest, and vice versa. These findings suggest that intrinsic stiffness is modulated simultaneously with reflex stiffness to optimize the control of balance. PMID:25570884
Arterial Stiffness and Cardiovascular Therapy
Jani?, Miodrag; Lunder, Mojca; abovi?, Mio
2014-01-01
The world population is aging and the number of old people is continuously increasing. Arterial structure and function change with age, progressively leading to arterial stiffening. Arterial stiffness is best characterized by measurement of pulse wave velocity (PWV), which is its surrogate marker. It has been shown that PWV could improve cardiovascular event prediction in models that included standard risk factors. Consequently, it might therefore enable better identification of populations at high-risk of cardiovascular morbidity and mortality. The present review is focused on a survey of different pharmacological therapeutic options for decreasing arterial stiffness. The influence of several groups of drugs is described: antihypertensive drugs (angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, calcium channel blockers, beta-blockers, diuretics, and nitrates), statins, peroral antidiabetics, advanced glycation end-products (AGE) cross-link breakers, anti-inflammatory drugs, endothelin-A receptor antagonists, and vasopeptidase inhibitors. All of these have shown some effect in decreasing arterial stiffness. Nevertheless, further studies are needed which should address the influence of arterial stiffness diminishment on major adverse cardiovascular and cerebrovascular events (MACCE). PMID:25170513
Bending Stiffness of Multiwall Sandwich
NASA Technical Reports Server (NTRS)
Blosser, M. L.
1983-01-01
An analytical and experimental study was carried out to understand the extensional and flexural behavior of multiwall sandwich, a metallic insulation composed of alternate layers of flat and dimpled foil. The multiwall sandwich was structurally analyzed by using several simplifying assumptions combined with a finite element analysis. The simplifying assumptions made in this analysis were evaluated by bending and tensile tests. Test results validate the assumption that flat sheets in compression do not significantly contribute to the flexural stiffness of multiwall sandwich for the multiwall geometry tested. However, calculations show that thicker flat sheets may contribute significantly to bending stiffness and cannot be ignored. Results of this analytical approach compare well with test data; both show that the extensional stiffness of the dimpled sheet in he 0 deg direction is about 30 percent of that for a flat sheet, and that in the 45 deg direction, it is about 10 percent. The analytical and experimental multiwall bending stiffness showed good agreement for the particular geometry tested.
Arterial stiffness: a brief review
Shirwany, Najeeb A; Zou, Ming-hui
2010-01-01
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. PMID:20802505
Numerical Simulation of Callus Healing for Optimization of Fracture Fixation Stiffness
Steiner, Malte; Claes, Lutz; Ignatius, Anita; Simon, Ulrich; Wehner, Tim
2014-01-01
The stiffness of fracture fixation devices together with musculoskeletal loading defines the mechanical environment within a long bone fracture, and can be quantified by the interfragmentary movement. In vivo results suggested that this can have acceleratory or inhibitory influences, depending on direction and magnitude of motion, indicating that some complications in fracture treatment could be avoided by optimizing the fixation stiffness. However, general statements are difficult to make due to the limited number of experimental findings. The aim of this study was therefore to numerically investigate healing outcomes under various combinations of shear and axial fixation stiffness, and to detect the optimal configuration. A calibrated and established numerical model was used to predict fracture healing for numerous combinations of axial and shear fixation stiffness under physiological, superimposed, axial compressive and translational shear loading in sheep. Characteristic maps of healing outcome versus fixation stiffness (axial and shear) were created. The results suggest that delayed healing of 3 mm transversal fracture gaps will occur for highly flexible or very rigid axial fixation, which was corroborated by in vivo findings. The optimal fixation stiffness for ovine long bone fractures was predicted to be 10002500 N/mm in the axial and >300 N/mm in the shear direction. In summary, an optimized, moderate axial stiffness together with certain shear stiffness enhances fracture healing processes. The negative influence of one improper stiffness can be compensated by adjustment of the stiffness in the other direction. PMID:24991809
“An Impediment to Living Life”: Why and How Should We Measure Stiffness in Polymyalgia Rheumatica?
Mackie, Sarah Louise; Hughes, Rodney; Walsh, Margaret; Day, John; Newton, Marion; Pease, Colin; Kirwan, John; Morris, Marianne
2015-01-01
Objectives To explore patients’ concepts of stiffness in polymyalgia rheumatica (PMR), and how they think stiffness should be measured. Methods Eight focus groups were held at three centres involving 50 patients with current/previous PMR. Each group had at least one facilitator and one rapporteur making field notes. An interview schedule was used to stimulate discussion. Interviews were recorded, transcribed and analysed using an inductive thematic approach. Results Major themes identified were: symptoms: pain, stiffness and fatigue; functional impact; impact on daily schedule; and approaches to measurement. The common subtheme for the experience of stiffness was “difficulty in moving”, and usually considered as distinct from the experience of pain, albeit with a variable overlap. Some participants felt stiffness was the “overwhelming” symptom, in that it prevented them carrying out “fundamental activities” and “generally living life”. Diurnal variation in stiffness was generally described in relation to the daily schedule but was not the same as stiffness severity. Some participants suggested measuring stiffness using a numeric rating scale or a Likert scale, while others felt that it was more relevant and straightforward to measure difficulty in performing everyday activities rather than about stiffness itself. Conclusions A conceptual model of stiffness in PMR is presented where stiffness is an important part of the patient experience and impacts on their ability to live their lives. Stiffness is closely related to function and often regarded as interchangeable with pain. From the patients’ perspective, visual analogue scales measuring pain and stiffness were not the most useful method for reporting stiffness; participants preferred numerical rating scales, or assessments of function to reflect how stiffness impacts on their daily lives. Assessing function may be a pragmatic solution to difficulties in quantifying stiffness. PMID:25955770
Substrate Stiffness Regulates Filopodial Activities in Lung Cancer Cells
Liou, Yu-Ren; Torng, Wen; Kao, Yu-Chiu; Sung, Kung-Bin; Lee, Chau-Hwang; Kuo, Po-Ling
2014-01-01
Microenvironment stiffening plays a crucial role in tumorigenesis. While filopodia are generally thought to be one of the cellular mechanosensors for probing environmental stiffness, the effects of environmental stiffness on filopodial activities of cancer cells remain unclear. In this work, we investigated the filopodial activities of human lung adenocarcinoma cells CL1-5 cultured on substrates of tunable stiffness using a novel platform. The platform consists of an optical system called structured illumination nano-profilometry, which allows time-lapsed visualization of filopodial activities without fluorescence labeling. The culturing substrates were composed of polyvinyl chloride mixed with an environmentally friendly plasticizer to yield Young's modulus ranging from 20 to 60 kPa. Cell viability studies showed that the viability of cells cultured on the substrates was similar to those cultured on commonly used elastomers such as polydimethylsiloxane. Time-lapsed live cell images were acquired and the filopodial activities in response to substrates with varying degrees of stiffness were analyzed. Statistical analyses revealed that lung cancer cells cultured on softer substrates appeared to have longer filopodia, higher filopodial densities with respect to the cellular perimeter, and slower filopodial retraction rates. Nonetheless, the temporal analysis of filopodial activities revealed that whether a filopodium decides to extend or retract is purely a stochastic process without dependency on substrate stiffness. The discrepancy of the filopodial activities between lung cancer cells cultured on substrates with different degrees of stiffness vanished when the myosin II activities were inhibited by treating the cells with blebbistatin, which suggests that the filopodial activities are closely modulated by the adhesion strength of the cells. Our data quantitatively relate filopodial activities of lung cancer cells with environmental stiffness and should shed light on the understanding and treatment of cancer progression and metastasis. PMID:24587021
Elastic metamaterial beam with remotely tunable stiffness
NASA Astrophysics Data System (ADS)
Qian, Wei; Yu, Zhengyue; Wang, Xiaole; Lai, Yun; Yellen, Benjamin B.
2016-02-01
We demonstrate a dynamically tunable elastic metamaterial, which employs remote magnetic force to adjust its vibration absorption properties. The 1D metamaterial is constructed from a flat aluminum beam milled with a linear array of cylindrical holes. The beam is backed by a thin elastic membrane, on which thin disk-shaped permanent magnets are mounted. When excited by a shaker, the beam motion is tracked by a Laser Doppler Vibrometer, which conducts point by point scanning of the vibrating element. Elastic waves are unable to propagate through the beam when the driving frequency excites the first elastic bending mode in the unit cell. At these frequencies, the effective mass density of the unit cell becomes negative, which induces an exponentially decaying evanescent wave. Due to the non-linear elastic properties of the membrane, the effective stiffness of the unit cell can be tuned with an external magnetic force from nearby solenoids. Measurements of the linear and cubic static stiffness terms of the membrane are in excellent agreement with experimental measurements of the bandgap shift as a function of the applied force. In this implementation, bandgap shifts by as much as 40% can be achieved with ˜30 mN of applied magnetic force. This structure has potential for extension in 2D and 3D, providing a general approach for building dynamically tunable elastic metamaterials for applications in lensing and guiding elastic waves.
STIFF: Converting Scientific FITS Images to TIFF
NASA Astrophysics Data System (ADS)
Bertin, Emmanuel
2011-10-01
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.
NASA Astrophysics Data System (ADS)
Newman, Ezra Ted; Penrose, Roger
2009-06-01
The spin-coefficient formalism (SC formalism) (also known in the literature as Newman-Penrose formalism (NP formalism) ) is a commonly used technique based on the use of null tetrads, with ideas taken from 2-component spinors, for the detailed treatment of 4-dimensional space-times satisfying the equations of Einstein's theory of general relativity.
NASA Astrophysics Data System (ADS)
Gunduz, Aydin; Singh, Rajendra
2013-10-01
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.
Engineering tools for variable stiffness vibration suppression and isolation
NASA Astrophysics Data System (ADS)
Winthrop, Michael F.
With the advent of smart materials, the concept of semi-active control or dynamic control of stiffness and/or damping for vibration control of structures has become practical and has seen limited use. Semi-active control has advantages over active and passive control methods, since it provides almost as much capability as active control while requiring much less power. Its main disadvantage is its inherent nonlinearity, greatly complicating engineering design. The purpose of this research is to extend semi-active control vibration isolation tools and methods, considering applications for space launch and on-orbit systems. After surveying the literature, variable stiffness using a general on-off control law with constant damping is examined in several contexts. First, the single degree of freedom problem is solved in exact form and approximated for the initial value problem. Results include development of an optimal control policy for all possible variable stiffness settings and a large range of viscous damping settings, guaranteed stability regions, and new possibilities for fast settling time even with an overdamped system. Second, the sinusoidally forced problem was approximated and a near optimal control policy was formulated. Third, the results of the initial value problem were extended to two multi-degree of freedom problems. The problems examined are representative of a cross section of a simple space telescope structure and of a variable stiffness beam. Besides providing new engineering design tools and insight into the nonlinear behavior of variable stiffness concepts, the results open several future research possibilities.
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.; Mikulas, Martin M., Jr.
2009-01-01
Simple formulas for the buckling stress of homogeneous, specially orthotropic, laminated-composite cylinders are presented. The formulas are obtained by using nondimensional parameters and equations that facilitate general validation, and are validated against the exact solution for a wide range of cylinder geometries and laminate constructions. Results are presented that establish the ranges of the nondimensional parameters and coefficients used. General results, given in terms of the nondimensional parameters, are presented that encompass a wide range of geometries and laminate constructions. These general results also illustrate a wide spectrum of behavioral trends. Design-oriented results are also presented that provide a simple, clear indication of laminate composition on critical stress, critical strain, and axial stiffness. An example is provided to demonstrate the application of these results to thin-walled column designs.
Parameter estimation for stiff deterministic dynamical systems via ensemble Kalman filter
NASA Astrophysics Data System (ADS)
Arnold, Andrea; Calvetti, Daniela; Somersalo, Erkki
2014-10-01
A commonly encountered problem in numerous areas of applications is to estimate the unknown coefficients of a dynamical system from direct or indirect observations at discrete times of some of the components of the state vector. A related problem is to estimate unobserved components of the state. An egregious example of such a problem is provided by metabolic models, in which the numerous model parameters and the concentrations of the metabolites in tissue are to be estimated from concentration data in the blood. A popular method for addressing similar questions in stochastic and turbulent dynamics is the ensemble Kalman filter (EnKF), a particle-based filtering method that generalizes classical Kalman filtering. In this work, we adapt the EnKF algorithm for deterministic systems in which the numerical approximation error is interpreted as a stochastic drift with variance based on classical error estimates of numerical integrators. This approach, which is particularly suitable for stiff systems where the stiffness may depend on the parameters, allows us to effectively exploit the parallel nature of particle methods. Moreover, we demonstrate how spatial prior information about the state vector, which helps the stability of the computed solution, can be incorporated into the filter. The viability of the approach is shown by computed examples, including a metabolic system modeling an ischemic episode in skeletal muscle, with a high number of unknown parameters.
Carrier mediated reduction of stiffness in nanoindented crystalline Si(100)
NASA Astrophysics Data System (ADS)
Kataria, S.; Dhara, Sandip; Dash, S.; Tyagi, A. K.
2015-07-01
We report the observation of carrier mediated decrease in the stiffness of crystalline (c)-Si(100) under nanoindentation. The apparent elastic moduli of heavily doped (1 1021 cm-3) p- and n-type c-Si are observed to be lower by 5.3%-7.5% than the estimated value for intrinsic (1 1014 cm-3) c-Si. The deviation observed with respect to elastic modulus remarkably matches with the estimated value while considering the electronic elastic strain effect on carrier concentration as an influence of negative pressure coefficient of band gap for Si (?-X). The value is predominantly higher than the reported value of a decrease of 1%-3% in stiffness as an effect of impurity in c-Si.
Dynamic phototuning of 3D hydrogel stiffness
Stowers, Ryan S.; Allen, Shane C.; Suggs, Laura J.
2015-01-01
Hydrogels are widely used as in vitro culture models to mimic 3D cellular microenvironments. The stiffness of the extracellular matrix is known to influence cell phenotype, inspiring work toward unraveling the role of stiffness on cell behavior using hydrogels. However, in many biological processes such as embryonic development, wound healing, and tumorigenesis, the microenvironment is highly dynamic, leading to changes in matrix stiffness over a broad range of timescales. To recapitulate dynamic microenvironments, a hydrogel with temporally tunable stiffness is needed. Here, we present a system in which alginate gel stiffness can be temporally modulated by light-triggered release of calcium or a chelator from liposomes. Others have shown softening via photodegradation or stiffening via secondary cross-linking; however, our system is capable of both dynamic stiffening and softening. Dynamic modulation of stiffness can be induced at least 14 d after gelation and can be spatially controlled to produce gradients and patterns. We use this system to investigate the regulation of fibroblast morphology by stiffness in both nondegradable gels and gels with degradable elements. Interestingly, stiffening inhibits fibroblast spreading through either mesenchymal or amoeboid migration modes. We demonstrate this technology can be translated in vivo by using deeply penetrating near-infrared light for transdermal stiffness modulation, enabling external control of gel stiffness. Temporal modulation of hydrogel stiffness is a powerful tool that will enable investigation of the role that dynamic microenvironments play in biological processes both in vitro and in well-controlled in vivo experiments. PMID:25646417
Palombo, Carlo; Kozakova, Michaela
2016-02-01
Arterial stiffness results from a degenerative process affecting mainly the extracellular matrix of elastic arteries under the effect of aging and risk factors. Changes in extracellular matrix proteins and in the mechanical properties of the vessel wall related to arterial stiffening may activate number of mechanisms involved also in the process of atherosclerosis. Several noninvasive methods are now available to estimate large artery stiffness in the clinical setting, including carotid-femoral pulse wave velocity, the reference for aortic stiffness estimate, and local distensibility measures of superficial arteries, namely carotid and femoral. An independent predictive value of arterial stiffness for cardiovascular events has been demonstrated in general as well as in selected populations, and reference values adjusted for age and blood pressure have been established. Thus, arterial stiffness is emerging as an interesting tissue biomarker for cardiovascular risk stratification and estimation of the individual "biological age". This paper overviews the mechanisms accounting for development and progression of arterial stiffness and for associations between arterial stiffness, atherosclerotic burden and incident cardiovascular events, summarizes the evidence and caveat for clinical use of stiffness as surrogate marker of cardiovascular risk, and briefly outlines some emerging methods for large artery stiffness characterization. PMID:26643779
Difference methods for stiff delay differential equations. [DDESUB, in FORTRAN
Roth, Mitchell G.
1980-12-01
Delay differential equations of the form y'(t) = f(y(t), z(t)), where z(t) = (y/sub 1/(..cap alpha../sub 1/(y(t))),..., y/sub n/(..cap alpha../sub n/(y(t))))/sup T/ and ..cap alpha../sub i/(y(t)) less than or equal to t, arise in many scientific and engineering fields when transport lags and propagation times are physically significant in a dynamic process. Difference methods for approximating the solution of stiff delay systems require special stability properties that are generalizations of those employed for stiff ordinary differential equations. By use of the model equation y'(t) = py(t) + qy(t-1), with complex p and q, the definitions of A-stability, A( )-stability, and stiff stability have been generalize to delay equations. For linear multistep difference formulas, these properties extend directly from ordinary to delay equations. This straight forward extension is not true for implicit Runge-Kutta methods, as illustrated by the midpoint formula, which is A-stable for ordinary equations, but not for delay equations. A computer code for stiff delay equations was developed using the BDF. 24 figures, 5 tables.
Modifiable Risk Factors for Increased Arterial Stiffness in Outpatient Nephrology
Elewa, Usama; Fernandez-Fernandez, Beatriz; Alegre, Raquel; Sanchez-Nio, Maria D.; Mahillo-Fernndez, Ignacio; Perez-Gomez, Maria Vanessa; El-Fishawy, Hussein; Belal, Dawlat; Ortiz, Alberto
2015-01-01
Arterial stiffness, as measured by pulse wave velocity (PWV), is an independent predictor of cardiovascular events and mortality. Arterial stiffness increases with age. However, modifiable risk factors such as smoking, BP and salt intake also impact on PWV. The finding of modifiable risk factors may lead to the identification of treatable factors, and, thus, is of interest to practicing nephrologist. We have now studied the prevalence and correlates of arterial stiffness, assessed by PWV, in 191 patients from nephrology outpatient clinics in order to identify modifiable risk factors for arterial stiffness that may in the future guide therapeutic decision-making. PWV was above normal levels for age in 85/191 (44.5%) patients. Multivariate analysis showed that advanced age, systolic BP, diabetes mellitus, serum uric acid and calcium polystyrene sulfonate therapy or calcium-containing medication were independent predictors of PWV. A new parameter, Delta above upper limit of normal PWV (Delta PWV) was defined to decrease the weight of age on PWV values. Delta PWV was calculated as (measured PWV) - (upper limit of the age-adjusted PWV values for the general population). MeanSD Delta PWV was 0.761.60 m/sec. In multivariate analysis, systolic blood pressure, active smoking and calcium polystyrene sulfonate therapy remained independent predictors of higher delta PWV, while age, urinary potassium and beta blocker therapy were independent predictors of lower delta PWV. In conclusion, arterial stiffness was frequent in nephrology outpatients. Systolic blood pressure, smoking, serum uric acid, calcium-containing medications, potassium metabolism and non-use of beta blockers are modifiable factors associated with increased arterial stiffness in Nephrology outpatients. PMID:25880081
Simulation methods with extended stability for stiff biochemical Kinetics
2010-01-01
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, τ, 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 τ 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 τ-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 τ grows. Results In this paper we extend Poisson τ-leap methods to a general class of Runge-Kutta (RK) τ-leap methods. We show that with the proper selection of the coefficients, the variance of the extended τ-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 τ-leap method. The approach paves the way to explore new multiscale methods to simulate (bio)chemical systems. PMID:20701766
Analysis and Design of Variable Stiffness Composite Cylinders
NASA Technical Reports Server (NTRS)
Tatting, Brian F.; Guerdal, Zafer
1998-01-01
An investigation of the possible performance improvements of thin circular cylindrical shells through the use of the variable stiffness concept is presented. The variable stiffness concept implies that the stiffness parameters change spatially throughout the structure. This situation is achieved mainly through the use of curvilinear fibers within a fiber-reinforced composite laminate, though the possibility of thickness variations and discrete stiffening elements is also allowed. These three mechanisms are incorporated into the constitutive laws for thin shells through the use of Classical Lamination Theory. The existence of stiffness variation within the structure warrants a formulation of the static equilibrium equations from the most basic principles. The governing equations include sufficient detail to correctly model several types of nonlinearity, including the formation of a nonlinear shell boundary layer as well as the Brazier effect due to nonlinear bending of long cylinders. Stress analysis and initial buckling estimates are formulated for a general variable stiffness cylinder. Results and comparisons for several simplifications of these highly complex governing equations are presented so that the ensuing numerical solutions are considered reliable and efficient enough for in-depth optimization studies. Four distinct cases of loading and stiffness variation are chosen to investigate possible areas of improvement that the variable stiffness concept may offer over traditional constant stiffness and/or stiffened structures. The initial investigation deals with the simplest solution for cylindrical shells in which all quantities are constant around the circumference of the cylinder. This axisymmetric case includes a stiffness variation exclusively in the axial direction, and the only pertinent loading scenarios include constant loads of axial compression, pressure, and torsion. The results for these cases indicate that little improvement over traditional laminates exists through the use of curvilinear fibers, mainly due to the presence of a weak link area within the stiffness variation that limits the ultimate load that the structure can withstand. Rigorous optimization studies reveal that even though slight increases in the critical loads can be produced for designs with an arbitrary variation of the fiber orientation angle, the improvements are not significant when compared to traditional design techniques that utilize ring stiffeners and frames. The second problem that is studied involves arbitrary loading of a cylinder with a stiffness variation that changes only in the circumferential direction. The end effects of the cylinder are ignored, so that the problem takes the form of an analysis of a cross-section for a short cylinder segment. Various load cases including axial compression, pressure, torsion, bending, and transverse shear forces are investigated. It is found that the most significant improvements in load-carrying capability exist for cases which involve loads that also vary around the circumference of the shell, namely bending and shear forces. The stiffness variation of the optimal designs contribute to the increased performance in two ways: lowering the stresses in the critical areas through redistribution of the stresses; and providing a relatively stiff region that alters the buckling behavior of the structure. These results lead to an in-depth optimization study involving weight optimization of a fuselage structure subjected to typical design constraints. Comparisons of the curvilinear fiber format to traditional stiffened structures constructed of isotropic and composite materials are included. It is found that standard variable stiffness designs are quite comparable in terms of weight and load-carrying capability yet offer the added advantage of tailorability of distinct regions of the structure that experience drastically different loading conditions. The last two problems presented in this work involve the nonlinear phenomenon of long tubes under bending. Though this scenario is not as applicable to fuselage structures as the previous problems, the mechanisms that produce the nonlinear effect are ideally suited to be controlled by the variable stiffness concept. This is due to the fact that the dominating influence for long cylinders under bending is the ovalization of the cross-section, which is governed mainly by the stiffness parameters of the cylindrical shell. Possible improvement of the critical buckling moments for these structures is investigated using either a circumferential or axial stiffness variation. For the circumferential case involving infinite length cylinders, it is found that slight improvements can be observed by designing structures that resist the cross-sectional deformation yet do not detract from the buckling resistance at the critical location. The results also indicate that buckling behavior is extremely dependent on cylinder length. This effect is most easily seen in the solution of finite length cylinders under bending that contain an axial stiffness variation. For these structures, the only mechanism that exhibits improved response are those that effectively shorten the length of the cylinder, thus reducing the cross-sectional deformation due to the forced restraint at the ends. It was found that the use of curvilinear fibers was not able to achieve this effect in sufficient degree to resist the deformation, but that ring stiffeners produced the desired response admirably. Thus, it is shown that the variable stiffness concept is most effective at improving the bending response of long cylinders through the use of a circumferential stiffness variation.
Prevention and treatment of elbow stiffness.
Evans, Peter J; Nandi, Sumon; Maschke, Steven; Hoyen, Harry A; Lawton, Jeffrey N
2009-04-01
The elbow is as prone to stiffness as it is essential for upper-extremity function. The elbow is a highly constrained synovial hinge joint that frequently becomes stiff after injury. Elbow contracture is challenging to treat, and therefore prevention is of paramount importance. When this approach fails, nonoperative followed by operative treatment modalities can be pursued. In the future, efforts to prevent and treat elbow stiffness may target the basic science mechanisms involved. PMID:19345886
Arterial Stiffness and ?-Amyloid Progression in Nondemented Elderly Adults
Hughes, Timothy M.; Kuller, Lewis H.; Barinas-Mitchell, Emma J. M.; McDade, Eric M.; Klunk, William E.; Cohen, Ann D.; Mathis, Chester A.; DeKosky, Steven T.; Price, Julie C.; Lopez, Oscar L.
2014-01-01
IMPORTANCE Recent studies show that cerebral ?-amyloid (A?) deposition is associated with blood pressure and measures of arterial stiffness in nondemented individuals. OBJECTIVE To examine the association between measures of arterial stiffness and change in A? deposition over time. DESIGN, SETTING, AND PARTICIPANTS Deposition of A? was determined in a longitudinal observational study of aging by positron emission tomography using the Pittsburgh compound B twice 2 years apart in 81 nondemented individuals 83 years and older. Arterial stiffness was measured with a noninvasive and automated waveform analyzer at the time closest to the second positron emission tomography scan. All measures were performed under standardized conditions. Pulse wave velocity (PWV) was measured in the central (carotid-femoral and heart-femoral PWV), peripheral (femoral-ankle PWV), and mixed (brachial-ankle PWV) vascular beds. MAIN OUTCOMES AND MEASURES The change in A? deposition over 2 years was calculated from the 81 individuals with repeat A?-positron emission tomography. RESULTS The proportion of A?-positive individuals increased from 48% at baseline to 75% at follow-up. Brachial-ankle PWV was significantly higher among A?-positive participants at baseline and follow-up. Femoral-ankle PWV was only higher among A?-positive participants at follow-up. Measures of central stiffness and blood pressure were not associated with A? status at baseline or follow-up, but central stiffness was associated with a change in A? deposition over time. Each standard deviation increase in central stiffness (carotid-femoral PWV, P = .001; heart-femoral PWV, P = .004) was linked with increases in A? deposition over 2 years. CONCLUSIONS AND RELEVANCE This study showed that A? deposition increases with age in nondemented individuals and that arterial stiffness is strongly associated with the progressive deposition of A? in the brain, especially in this age group. The association between A? deposition changes over time and generalized arterial stiffness indicated a relationship between the severity of subclinical vascular disease and progressive cerebral A? deposition. PMID:24687165
The fully implicit stochastic- ? method for stiff stochastic differential equations
NASA Astrophysics Data System (ADS)
Safique Ahmad, Sk.; Chandra Parida, Nigam; Raha, Soumyendu
2009-12-01
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.
A novel assessment technique for measuring ankle orientation and stiffness.
Zhang, Mingming; Davies, T Claire; Nandakumar, Anoop; Quan Xie, Sheng
2015-09-18
The measurement of ankle orientation and stiffness can provide insight into improvements and allows for effective monitoring during a rehabilitation program. Existing assessment techniques have a variety of limitations. Dynamometer based methods rely on manual manipulation. The use of torque meter is usually for single degree-of-freedom (DOF) devices. This study proposes a novel ankle assessment technique that can be used for multiple DOFs devices working in both manual and automatic modes using the position sensor and the multi-axis load cell. As a preliminary evaluation, an assessment device for ankle dorsiflexion and plantarflexion was constructed. Nine subjects participated to evaluate the effectiveness of the assessment device in determining ankle orientation and stiffness. The measured ankle orientation was consistent with that from the NDI Polaris optical tracking system. The measured ankle torque and stiffness compared well with published data. The test-retest reliability was high with intraclass correlation coefficient (ICC2, 1) values greater than 0.846 and standard error of measurement (SEM) less than 1.38. PMID:26159061
Nonparticipatory Stiffness in the Male Perioral Complex
ERIC Educational Resources Information Center
Chu, Shin-Ying; Barlow, Steven M.; Lee, Jaehoon
2009-01-01
Purpose: The objective of this study was to extend previous published findings in the authors' laboratory using a new automated technology to quantitatively characterize nonparticipatory perioral stiffness in healthy male adults. Method: Quantitative measures of perioral stiffness were sampled during a nonparticipatory task using a
Nonparticipatory Stiffness in the Male Perioral Complex
ERIC Educational Resources Information Center
Chu, Shin-Ying; Barlow, Steven M.; Lee, Jaehoon
2009-01-01
Purpose: The objective of this study was to extend previous published findings in the authors' laboratory using a new automated technology to quantitatively characterize nonparticipatory perioral stiffness in healthy male adults. Method: Quantitative measures of perioral stiffness were sampled during a nonparticipatory task using a…
Spinal stiffness changes throughout the respiratory cycle.
Shirley, D; Hodges, P W; Eriksson, A E M; Gandevia, S C
2003-10-01
Posteroanterior stiffness of the lumbar spine is influenced by factors, including trunk muscle activity and intra-abdominal pressure (IAP). Because these factors vary with breathing, this study investigated whether stiffness is modulated in a cyclical manner with respiration. A further aim was to investigate the relationship between stiffness and IAP or abdominal and paraspinal muscle activity. Stiffness was measured from force-displacement responses of a posteroanterior force applied over the spinous process of L2 and L4. Recordings were made of IAP and electromyographic activity from L4/L2 erector spinae, abdominal muscles, and chest wall. Stiffness was measured with the lung volume held at the extremes of tidal volume and at greater and lesser volumes. Stiffness at L4 and L2 increased above base-level values at functional residual capacity (L2 14.9 N/mm and L4 15.3 N/mm) with both inspiratory and expiratory efforts. The increase was related to the respiratory effort and was greatest during maximum expiration (L2 24.9 N/mm and L4 23.9 N/mm). The results indicate that changes in trunk muscle activity and IAP with respiratory efforts modulate spinal stiffness. In addition, the diaphragm may augment spinal stiffness via attachment of its crural fibers to the lumbar vertebrae. PMID:12970374
Spontaneous wrinkle branching by gradient stiffness
NASA Astrophysics Data System (ADS)
Ni, Yong; Yang, Dong; He, Linghui
2012-09-01
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 Fppl-von Krmn 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.
Spontaneous wrinkle branching by gradient stiffness.
Ni, Yong; Yang, Dong; He, Linghui
2012-09-01
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 Fppl-von Krmn 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. PMID:23030926
Rolling Element Bearing Stiffness Matrix Determination (Presentation)
Guo, Y.; Parker, R.
2014-01-01
Current theoretical bearing models differ in their stiffness estimates because of different model assumptions. In this study, a finite element/contact mechanics model is developed for rolling element bearings with the focus of obtaining accurate bearing stiffness for a wide range of bearing types and parameters. A combined surface integral and finite element method is used to solve for the contact mechanics between the rolling elements and races. This model captures the time-dependent characteristics of the bearing contact due to the orbital motion of the rolling elements. A numerical method is developed to determine the full bearing stiffness matrix corresponding to two radial, one axial, and two angular coordinates; the rotation about the shaft axis is free by design. This proposed stiffness determination method is validated against experiments in the literature and compared to existing analytical models and widely used advanced computational methods. The fully-populated stiffness matrix demonstrates the coupling between bearing radial, axial, and tilting bearing deflections.
Non-crossbridge calcium-dependent stiffness in slow and fast skeletal fibres from mouse muscle.
Nocella, Marta; Colombini, Barbara; Bagni, Maria Angela; Bruton, Joseph; Cecchi, Giovanni
2012-03-01
We showed previously that force development in frog and FDB mouse skeletal muscle fibres is preceded by an increase of fibre stiffness occurring well before crossbridge attachment and force generation. This stiffness increase, referred to as static stiffness, is due to a Ca(2+)-dependent stiffening of a non-crossbridge sarcomere structure which we suggested could be attributed to the titin filaments. To investigate further the role of titin in static stiffness, we measured static stiffness properties at 24 and 35C in soleus and EDL mouse muscle fibres which are known to express different titin isoforms. We found that static stiffness was present in both soleus and EDL fibres, however, its value was about five times greater in EDL than in soleus fibres. The rate of development of static stiffness on stimulation increased with temperature and was slightly faster in EDL than in soleus in agreement with previously published data on the time course of the intracellular Ca(2+) transients in these muscles. The present results show that the presence of a non-crossbridge Ca(2+)-dependent stiffening of the muscle fibre is a physiological general characteristic of skeletal muscle. Static stiffness depends on fibre type, being greater and developing faster in fast than in slow fibres. Our observations are consistent with the idea that titin stiffening on contraction improves the sarcomere structure stability. Such an action in fact seems to be more important in EDL fast fibre than in soleus slow fibres. PMID:22072314
What drives the translocation of stiff chains?
Zandi, Roya; Reguera, David; Rudnick, Joseph; Gelbart, William M.
2003-01-01
We study the dynamics of the passage of a stiff chain through a pore into a cell containing particles that bind reversibly to it. Using Brownian molecular dynamics simulations we investigate the mean first-passage time as a function of the length of the chain inside for different concentrations of binding particles. As a consequence of the interactions with these particles, the chain experiences a net force along its length whose calculated value from the simulations accounts for the velocity at which it enters the cell. This force can in turn be obtained from the solution of a generalized diffusion equation incorporating an effective Langmuir adsorption free energy for the chain plus binding particles. These results suggest a role of binding particles in the translocation process that is in general quite different from that of a Brownian ratchet. Furthermore, nonequilibrium effects contribute significantly to the dynamics; e.g., the chain often enters the cell faster than particle binding can be saturated, resulting in a force several times smaller than the equilibrium value. PMID:12851462
Force, stiffness and hysteresis losses in high temperature superconducting bearings
NASA Astrophysics Data System (ADS)
Cansiz, Ahmet
The vertical and horizontal forces and associated stiffnesses on a permanent magnet above a high- temperature superconductor were measured during vertical and horizontal traverses in zero-field cooling and in field cooling. In field cooling and zero field cooling, the vertical stiffness showed history dependence. In field cooling, the vertical stiffness was exactly two times greater than the lateral stiffness at each height, with an experimental error of less than 1%. A frozen image model was used to calculate the vertical and horizontal forces and stiffnesses, and reasonable agreement with the data occurred for vertical or horizontal movements of the permanent magnet less than several min from the field cooling position. We have investigated the effect of high temperature superconductor films deposited on substrates that are placed above bulk high temperature superconductors in an attempt to reduce rotational drag in superconducting bearings composed of a permanent magnet levitated above the film/bulk combination. According to the critical state model, hysteresis loss is inversely proportional to critical current density and because films typically have much higher critical current density than those of bulks, the film/bulk combination was expected to reduce rotational losses by at least one order of magnitude in the coefficient of friction, which in turn is a measure of the hysteresis losses. The experimental results showed that contrary to expectation, the rotational losses are increased by the film. Increasing losses from using a thin film turned attention to whether the thin film was shielding the varying magnetic field caused by the rotation of inhomogenous permanent magnet. For this reason, an ac coil was placed above the thin film HTS and the magnetic field on the other side of the film was measured with a pick-up coil. The experimental results showed that the thin film provides good shielding when the coil axis is perpendicular to the film surface whereas there is poor shielding when the coil is parallel to the surface. We have also investigated the vibration characteristic of the levitated permanent magnet over HTS for different cooling height and these properties were incorporated with vertical and lateral stiffnesses obtained in static measurements.
Nonlinear and tangent stiffness of imperfect beam columns
NASA Technical Reports Server (NTRS)
Anderson, M. S.
1982-01-01
A curved member under axial load is analyzed using beam column theory to determine nonlinear response and the tangent stiffness associated with small displacements from the nonlinear state. Such a result is suitable for incorporation into a general nonlinear analysis using a corotational coordinate system to describe the rigid body type motion of individual members. The method is applied to buckling problems. Several examples are given to show the accuracy of the method.
The Difference between Stiffness and Quasi-stiffness in the Context of Biomechanical Modeling
Rouse, Elliott J.; Gregg, Robert D.; Hargrove, Levi J.; Sensinger, Jonathon W.
2014-01-01
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
The difference between stiffness and quasi-stiffness in the context of biomechanical modeling.
Rouse, Elliott J; Gregg, Robert D; Hargrove, Levi J; Sensinger, Jonathon W
2013-02-01
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
Stiff Coatings on Compliant Biofibers
Holten-Andersen, Niels; Zhao, Hua; Waite, J. Herbert
2009-01-01
For lasting holdfast attachment, the mussel Mytilus californianus coats its byssal threads with a protective cuticle 2-5 μm thick that is 4-6 times stiffer than the underlying collagen fibers. Although cuticle hardness (0.1 GPa) and stiffness (2 GPa) resemble those observed in related mussels, a more effective dispersion of microdamage enables M. californianus byssal threads to sustain strains to almost 120% before cuticle rupture occurs. Underlying factors for the superior damage tolerance of the byssal cuticle were explored in its microarchitecture and in the cuticular protein, mcfp-1. Cuticle microstructure was distinctly granular, with granule diameters (∼200 nm) only a quarter of those in M. galloprovincialis cuticle, for example. Compared with homologous proteins in related mussel species, mcfp-1 from M. californianus had a similar mass (∼92 kDa) and number of tandemly repeated decapeptides, and contained the same post-translational modifications, namely, trans-4-hydroxyproline, trans-2,3-cis-3,4-dihydroxyproline, and 3,4-dihydroxyphenylalanine (Dopa). The prominence of isoleucine in mcfp-1, however, distinguished it from homologues in other species. The complete protein sequence deduced from cDNAs for two related variants revealed a highly conserved consensus decapeptide PKISYPPTYK that is repeated 64 times and differs slightly from the consensus peptide (AKPSYPPTYK) of both M. galloprovincialis and M. edulis proteins. PMID:19220048
Wave Propagation of Myocardial Stretch: Correlation with Myocardial Stiffness
Pislaru, Cristina; Pellikka, Patricia A.; Pislaru, Sorin V.
2015-01-01
The mechanism of flow propagation during diastole in the left ventricle (LV) has been well described. Little is known about the associated waves propagating along the heart wall s. These waves may have a mechanism similar to pulse wave propagation in arteries. The major goal of the study was to evaluate the effect of myocardial stiffness and preload on this wave transmission. Methods Longitudinal late diastolic deformation and wave speed (Vp) of myocardial stretch in the anterior LV wall were measured using sonomicrometry in sixteen pigs. Animals with normal and altered myocardial stiffness (acute myocardial infarction) were studied with and without preload alterations. Elastic modulus estimated from Vp (EVP; Moens-Korteweg equation) was compared to incremental elastic modulus obtained from exponential end -diastolic stress-strain relation (ESS). Myocardial distensibility and ?-and ?-coefficients of stress-strain relations were calculated. Results Vp was higher at reperfusion compared to baseline (2.61.3 m/s vs. 1.30.4 m/s; p=0.005) and best correlated with ESS (r 2=0.80, p<0.0001), ?-coefficient (r2=0.78, p<0.0001), distensibility (r2=0.47, p=0.005), and wall thickness/diameter ratio (r2=0.42, p=0.009). Elastic moduli (EVP and ESS) were strongly correlated (r2=0.83, p<0.0001). Increasing preload increased Vp and EVP and decreased distensibility. At multivariate analysis, ESS, wall thickness, and end-diastolic and systolic LV pressures were independent predictors of Vp (r2model=0.83, p<0.0001). Conclusions The main determinants of wave propagation of longitudinal myocardial stretch were myocardial stiffness and LV geometry and pressure. This local wave speed could potentially be measured noninvasively by echocardiography. PMID:25193091
Wave propagation of myocardial stretch: correlation with myocardial stiffness.
Pislaru, Cristina; Pellikka, Patricia A; Pislaru, Sorin V
2014-01-01
The mechanism of flow propagation during diastole in the left ventricle (LV) has been well described. Little is known about the associated waves propagating along the heart walls. These waves may have a mechanism similar to pulse wave propagation in arteries. The major goal of the study was to evaluate the effect of myocardial stiffness and preload on this wave transmission. Longitudinal late diastolic deformation and wave speed (Vp) of myocardial stretch in the anterior LV wall were measured using sonomicrometry in 16 pigs. Animals with normal and altered myocardial stiffness (acute myocardial infarction) were studied with and without preload alterations. Elastic modulus estimated from Vp (E VP; Moens-Korteweg equation) was compared to incremental elastic modulus obtained from exponential end-diastolic stress-strain relation (E SS). Myocardial distensibility and α- and β-coefficients of stress-strain relations were calculated. Vp was higher at reperfusion compared to baseline (2.6 ± 1.3 vs. 1.3 ± 0.4 m/s; p = 0.005) and best correlated with E SS (r2 = 0.80, p < 0.0001), β-coefficient (r2 = 0.78, p < 0.0001), distensibility (r2 = 0.47, p = 0.005), and wall thickness/diameter ratio (r2 = 0.42, p = 0.009). Elastic moduli (E VP and E SS) were strongly correlated (r2 = 0.83, p < 0.0001). Increasing preload increased Vp and E VP and decreased distensibility. At multivariate analysis, E SS, wall thickness, and end-diastolic and systolic LV pressures were independent predictors of Vp (r2 model = 0.83, p < 0.0001). In conclusion, the main determinants of wave propagation of longitudinal myocardial stretch were myocardial stiffness and LV geometry and pressure. This local wave speed could potentially be measured noninvasively by echocardiography. PMID:25193091
Physical inactivity and arterial stiffness in COPD
Sievi, Noriane A; Franzen, Daniel; Kohler, Malcolm; Clarenbach, Christian F
2015-01-01
Background Arterial stiffness is an important predictor of cardiovascular risk besides classic cardiovascular risk factors. Previous studies showed that arterial stiffness is increased in patients with COPD compared to healthy controls and exercise training may reduce arterial stiffness. Since physical inactivity is frequently observed in patients with COPD and exercise training may improve arterial stiffness, we hypothesized that low daily physical activity may be associated with increased arterial stiffness. Methods In 123 patients with COPD (72% men; mean [standard deviation] age: 62 [7.5] years; median [quartile] forced expiratory volume in 1 second 35 [27/65] %predicted), arterial stiffness was assessed by augmentation index (AI). Daily physical activity level (PAL) was measured by an activity monitor (SenseWear Pro) >1 week. The association between AI and PAL was investigated by univariate and multivariate regression analysis, taking into account disease-specific characteristics and comorbidities. Results Patients suffered from moderate (35%), severe (32%), and very severe (33%) COPD, and 22% were active smokers. Median (quartile) PAL was 1.4 (1.3/1.5) and mean (standard deviation) AI 26% (9.2%). PAL showed a negative association with AI (B=?9.32, P=0.017) independent of age, sex, blood pressure, and airflow limitation. Conclusion In COPD patients, a higher PAL seems to favorably influence arterial stiffness and therefore may reduce cardiovascular risk. Clinical Trial Registration http://www.ClinicalTrials.gov, NCT01527773 PMID:26392763
Stiff substrates enhance cultured neuronal network activity
Zhang, Quan-You; Zhang, Yan-Yan; Xie, Jing; Li, Chen-Xu; Chen, Wei-Yi; Liu, Bai-Lin; Wu, Xiao-an; Li, Shu-Na; Huo, Bo; Jiang, Lin-Hua; Zhao, Hu-Cheng
2014-01-01
The mechanical property of extracellular matrix and cell-supporting substrates is known to modulate neuronal growth, differentiation, extension and branching. Here we show that substrate stiffness is an important microenvironmental cue, to which mouse hippocampal neurons respond and integrate into synapse formation and transmission in cultured neuronal network. Hippocampal neurons were cultured on polydimethylsiloxane substrates fabricated to have similar surface properties but a 10-fold difference in Young's modulus. Voltage-gated Ca2+ channel currents determined by patch-clamp recording were greater in neurons on stiff substrates than on soft substrates. Ca2+ oscillations in cultured neuronal network monitored using time-lapse single cell imaging increased in both amplitude and frequency among neurons on stiff substrates. Consistently, synaptic connectivity recorded by paired recording was enhanced between neurons on stiff substrates. Furthermore, spontaneous excitatory postsynaptic activity became greater and more frequent in neurons on stiff substrates. Evoked excitatory transmitter release and excitatory postsynaptic currents also were heightened at synapses between neurons on stiff substrates. Taken together, our results provide compelling evidence to show that substrate stiffness is an important biophysical factor modulating synapse connectivity and transmission in cultured hippocampal neuronal network. Such information is useful in designing instructive scaffolds or supporting substrates for neural tissue engineering. PMID:25163607
Athletic Footwear, Leg Stiffness, and Running Kinematics
Bishop, Mark; Fiolkowski, Paul; Conrad, Bryan; Brunt, Denis; Horodyski, MaryBeth
2006-01-01
Context: The leg acts as a linear spring during running and hopping and adapts to the stiffness of the surface, maintaining constant total stiffness of the leg-surface system. Introducing a substance (eg, footwear) may affect the stiffness of the leg in response to changes in surface stiffness. Objective: To determine if the type of athletic footwear affects the regulation of leg stiffness in dynamic activities. Design: Repeated-measures design. Setting: Motion analysis laboratory. Patients or Other Participants: Nine healthy adults (age = 28 6.8 years, mass = 71.6 12.9 kg) free from lower extremity injuries. Intervention(s): Subjects hopped at 2.2 Hz on a forceplate under 3 footwear conditions (barefoot, low-cost footwear, high-cost footwear). Subjects ran on a treadmill at 2 speeds (2.23 m/s, 3.58 m/s) under the same footwear conditions. Main Outcome Measure(s): Limb stiffness was calculated from forceplate data. Kinematic data (knee and ankle angles at initial contact and peak joint excursion after contact) were collected during running. We calculated 1-way repeated-measures (stiffness) and 2-way (speed by footwear) repeated-measures analyses of variance (running kinematics) to test the dependent variables. Results: A significant increase in leg stiffness from the barefoot to the cushioned shoe condition was noted during hopping. When running shod, runners landed in more dorsiflexion but had less ankle motion than when running barefoot. No differences were seen between the types of shoes. The primary kinematic difference was identified as running speed increased: runners landed in more knee flexion. At the ankle, barefoot runners increased ankle motion to a significantly greater extent than did shod runners as speed increased. Conclusions: Footwear influences the maintenance of stiffness in the lower extremity during hopping and joint excursion at the ankle in running. Differences in cushioning properties of the shoes tested did not appear to be significant. PMID:17273463
Is the negative equivalent stiffness of a system possible?
NASA Astrophysics Data System (ADS)
Zhao, Mohan
2016-01-01
The negative stiffness concept is seldom encountered in high school courses as well as in college courses. This paper reports a system with negative equivalent stiffness, which is the most important component in constructing a quasi-zero stiffness isolator.
The viscoelastic stiffness model of seismicity
NASA Technical Reports Server (NTRS)
Cohen, S. C.
1978-01-01
A viscoelastic stiffness model of seismicity is developed by introducing a viscoelastic element into the stiffness model for fault dynamics. The introduction of this element permits modeling of transient anelastic deformations in response to stress loading and relaxation and provides a mechanism for partial stress recovery following an earthquake. As a consequence, several phenomena not present in elastic stiffness theory emerge. These include postseismic creep, foreshocks, and aftershocks. Numerical simulations of fault motion also reveal episodes of stable sliding, tertiary creep preceeding earthquakes, and long-term aseismic creep.
“Smooth Muscle Cell Stiffness Syndrome”—Revisiting the Structural Basis of Arterial Stiffness
Sehgel, Nancy L.; Vatner, Stephen F.; Meininger, Gerald A.
2015-01-01
In recent decades, the pervasiveness of increased arterial stiffness in patients with cardiovascular disease has become increasingly apparent. Though, this phenomenon has been well documented in humans and animal models of disease for well over a century, there has been surprisingly limited development in a deeper mechanistic understanding of arterial stiffness. Much of the historical literature has focused on changes in extracellular matrix proteins—collagen and elastin. However, extracellular matrix changes alone appear insufficient to consistently account for observed changes in vascular stiffness, which we observed in our studies of aortic stiffness in aging monkeys. This led us to examine novel mechanisms operating at the level of the vascular smooth muscle cell (VSMC)—that include increased cell stiffness and adhesion to extracellular matrix—which that may be interrelated with other mechanisms contributing to arterial stiffness. We introduce these observations as a new concept—the Smooth Muscle Cell Stiffness Syndrome (SMCSS)—within the field of arterial stiffness and posit that stiffening of vascular cells impairs vascular function and may contribute stiffening to the vasculature with aging and cardiovascular disease. Importantly, this review article revisits the structural basis of arterial stiffness in light of these novel findings. Such classification of SMCSS and its contextualization into our current understanding of vascular mechanics may be useful in the development of strategic therapeutics to directly target arterial stiffness. PMID:26635621
Programmable variable stiffness 2D surface design
NASA Astrophysics Data System (ADS)
Trabia, Sarah; Hwang, Taeseon; Yim, Woosoon
2014-03-01
Variable stiffness features can contribute to many engineering applications ranging from robotic joints to shock and vibration mitigation. In addition, variable stiffness can be used in the tactile feedback to provide the sense of touch to the user. A key component in the proposed device is the Biased Magnetorheological Elastomer (B-MRE) where iron particles within the elastomer compound develop a dipole interaction energy. A novel feature of this device is to introduce a field induced shear modulus bias via a permanent magnet which provides an offset with a current input to the electromagnetic control coil to change the compliance or modulus of a base elastomer in both directions (softer or harder). The B-MRE units can lead to the design of a variable stiffness surface. In this preliminary work, both computational and experimental results of the B-MRE are presented along with a preliminary design of the programmable variable stiffness surface design.
Vascular stiffness in insulin resistance and obesity
Jia, Guanghong; Aroor, Annayya R.; DeMarco, Vincent G.; Martinez-Lemus, Luis A.; Meininger, Gerald A.; Sowers, James R.
2015-01-01
Obesity, insulin resistance, and type 2 diabetes are associated with a substantially increased prevalence of vascular fibrosis and stiffness, with attendant increased risk of cardiovascular and chronic kidney disease. Although the underlying mechanisms and mediators of vascular stiffness are not well understood, accumulating evidence supports the role of metabolic and immune dysregulation related to increased adiposity, activation of the renin angiotensin aldosterone system, reduced bioavailable nitric oxide, increased vascular extracellular matrix (ECM) and ECM remodeling in the pathogenesis of vascular stiffness. This review will give a brief overview of the relationship between obesity, insulin resistance and increased vascular stiffness to provide a contemporary understanding of the proposed underlying mechanisms and potential therapeutic strategies. PMID:26321962
Determination of ball bearing dynamic stiffness
NASA Technical Reports Server (NTRS)
Beatty, R. F.; Rowan, B. F.
1982-01-01
The dynamic radial stiffness characteristics of rolling element bearings are currently determined by analytical methods that have not been experimentally verified. These bearing data are vital to rotating machinery design integrity because accurate critical speeds and rotor stability predictions are highly dependent on the bearing stiffness. A tester was designed capable of controlling the bearing axial preload, speed, and rotor unbalance. The rotor and support structures were constructed to permit critical speeds that are predominantly determined by a 57 mm test bearing. A curve of calculated critical speed versus stiffness was used to determine the actual bearing stiffness from the empirical data. The results of extensive testing are used to verify analytical predictions, increase confidence in existing bearing computer programs, and to serve as a data base for efforts to correct these programs.
Macroscopic stiffness of breast tumors predicts metastasis.
Fenner, Joseph; Stacer, Amanda C; Winterroth, Frank; Johnson, Timothy D; Luker, Kathryn E; Luker, Gary D
2014-01-01
Mechanical properties of tumors differ substantially from normal cells and tissues. Changes in stiffness or elasticity regulate pro-metastatic behaviors of cancer cells, but effects have been documented predominantly in isolated cells or in vitro cell culture systems. To directly link relative stiffness of tumors to cancer progression, we combined a mouse model of metastatic breast cancer with ex vivo measurements of bulk moduli of freshly excised, intact tumors. We found a high, inverse correlation between bulk modulus of resected tumors and subsequent local recurrence and metastasis. More compliant tumors were associated with more frequent, larger local recurrences and more extensive metastases than mice with relatively stiff tumors. We found that collagen content of resected tumors correlated with bulk modulus values. These data establish that relative differences in tumor stiffness correspond with tumor progression and metastasis, supporting further testing and development of tumor compliance as a prognostic biomarker in breast cancer. PMID:24981707
Macroscopic Stiffness of Breast Tumors Predicts Metastasis
Fenner, Joseph; Stacer, Amanda C.; Winterroth, Frank; Johnson, Timothy D.; Luker, Kathryn E.; Luker, Gary D.
2014-01-01
Mechanical properties of tumors differ substantially from normal cells and tissues. Changes in stiffness or elasticity regulate pro-metastatic behaviors of cancer cells, but effects have been documented predominantly in isolated cells or in vitro cell culture systems. To directly link relative stiffness of tumors to cancer progression, we combined a mouse model of metastatic breast cancer with ex vivo measurements of bulk moduli of freshly excised, intact tumors. We found a high, inverse correlation between bulk modulus of resected tumors and subsequent local recurrence and metastasis. More compliant tumors were associated with more frequent, larger local recurrences and more extensive metastases than mice with relatively stiff tumors. We found that collagen content of resected tumors correlated with bulk modulus values. These data establish that relative differences in tumor stiffness correspond with tumor progression and metastasis, supporting further testing and development of tumor compliance as a prognostic biomarker in breast cancer. PMID:24981707
Exercise, Vascular Stiffness, and Tissue Transglutaminase
Steppan, Jochen; Sikka, Gautam; Jandu, Simran; Barodka, Viachaslau; Halushka, Marc K.; Flavahan, Nicholas A.; Belkin, Alexey M.; Nyhan, Daniel; Butlin, Mark; Avolio, Alberto; Berkowitz, Dan E.; Santhanam, Lakshmi
2014-01-01
Background Vascular aging is closely associated with increased vascular stiffness. It has recently been demonstrated that decreased nitric oxide (NO)?induced S?nitrosylation of tissue transglutaminase (TG2) contributes to age?related vascular stiffness. In the current study, we tested the hypothesis that exercise restores NO signaling and attenuates vascular stiffness by decreasing TG2 activity and cross?linking in an aging rat model. Methods and Results Rats were subjected to 12 weeks of moderate aerobic exercise. Aging was associated with diminished phosphorylated endothelial nitric oxide synthase and phosphorylated vasodilator?stimulated phosphoprotein abundance, suggesting reduced NO signaling. TG2 cross?linking activity was significantly increased in old animals, whereas TG2 abundance remained unchanged. These alterations were attenuated in the exercise cohort. Simultaneous measurement of blood pressure and pulse wave velocity (PWV) demonstrated increased aortic stiffness in old rats, compared to young, at all values of mean arterial pressure (MAP). The PWV?MAP correlation in the old sedentary and old exercise cohorts was similar. Tensile testing of the vessels showed increased stiffness of the aorta in the old phenotype with a modest restoration of mechanical properties toward the young phenotype with exercise. Conclusions Increased vascular stiffness during aging is associated with decreased TG2 S?nitrosylation, increased TG2 cross?linking activity, and increased vascular stiffness likely the result of decreased NO bioavailability. In this study, a brief period of moderate aerobic exercise enhanced NO signaling, attenuated TG cross?linking activity, and reduced ex vivo tensile properties, but failed to reverse functional vascular stiffness in vivo, as measured by PWV. PMID:24721796
Stiff limb syndrome: a case report
2010-01-01
Introduction Stiff limb syndrome is a clinical feature of the stiff person syndrome, which is a rare and disabling neurologic disorder characterized by muscle rigidity and episodic spasms that involve axial and limb musculature. It is an autoimmune disorder resulting in a malfunction of aminobutyric acid mediated inhibitory networks in the central nervous system. We describe a patient diagnosed by neurological symptoms of stiff limb syndrome with a good outcome after treatment, and a review of the related literature. Case presentation A 49-year-old male patient presented with a progressive stiffness and painful spasms of his both legs resulting in a difficulty of standing up and walking. The diagnosis of stiff limb syndrome was supported by the dramatically positive response to treatment using diazepam 25 mg/day and baclofen 30 mg/day. Conclusion This clinical case highlights the importance of a therapeutic test to confirm the diagnosis of stiff limb syndrome especially when there is a high clinical suspicion with unremarkable electromyography PMID:20205913
Stiffness of Railway Soil-Steel Structures
NASA Astrophysics Data System (ADS)
Machelski, Czesław
2015-12-01
The considerable influence of the soil backfill properties and that of the method of compacting it on the stiffness of soil-steel structures is characteristic of the latter. The above factors (exhibiting randomness) become apparent in shell deformation measurements conducted during construction and proof test loading. A definition of soil-shell structure stiffness, calculated on the basis of shell deflection under the service load, is proposed in the paper. It is demonstrated that the stiffness is the inverse of the deflection influence function used in structural mechanics. The moving load methodology is shown to be useful for testing, since it makes it possible to map the shell deflection influence line also in the case of group loads (concentrated forces), as in bridges. The analyzed cases show that the shell's span, geometry (static scheme) and the height of earth fill influence the stiffness of the structure. The soil-steel structure's characteristic parameter in the form of stiffness k is more suitable for assessing the quality of construction works than the proposed in code geometric index ω applied to beam structures. As shown in the given examples, parameter k is more effective than stiffness parameter λ used to estimate the deformation of soil-steel structures under construction. Although the examples concern railway structures, the methodology proposed in the paper is suitable also for road bridges.
Study of a piecewise linear dynamic system with negative and positive stiffness
NASA Astrophysics Data System (ADS)
Zou, Keguan; Nagarajaiah, Satish
2015-05-01
The present paper mainly focuses on numerical and analytical study of a piecewise linear dynamic oscillator with negative stiffness followed by positive stiffness which has not been studied to date. The dynamic system of interest stems from a previous analytical and experimental research on adaptive negative stiffness for the purpose of seismic protection. Numerical algorithms meant specifically for simulating piecewise smooth (PWS) systems like this nonlinear system are studied. An appropriate combination of negative stiffness and adequate damping can reduce the peak restoring or transmitted force with a slightly larger peak displacement. Essentially, the negative stiffness system in a dynamic system is very beneficial in reducing the amount of force transmitted. The exact solution is derived for free vibration. A modified Lindstedt-Poincar method (modified L-P method) is adopted to derive approximate periodic solutions for the forced and damped system and its frequency-response curves are obtained through numerical simulation. The modified L-P solution obtained for the forced and damped case is found to agree well with the numerical results. In the piecewise linear dynamic system with initial negative stiffness followed by positive stiffness, it is found that the response remains bounded in a limit cycle. This system behaves similar to a van der Pol oscillator wherein negative damping is followed by positive damping. Presented herein is a special case as defined by the specified parameter ranges; thus, to make it more general future work is needed.
Stiffness and Confinement Ratios of SMA Wire Jackets for Confining Concrete
NASA Astrophysics Data System (ADS)
Choi, Eunsoo; Kim, Dong Joo; Youn, Heejung
2014-07-01
This article discusses the effects of the stiffness and confinement ratios of shape memory alloy (SMA) wire jackets on the behavior of confined concrete. SMA wire jackets are an effective confining material to improve concrete behavior; for example, by increasing peak strength and failure strain. The stiffness and confinement ratios of fiber-reinforced polymer jackets have been extensively discussed and their effects are well known. However, assessment of the stiffness and confinement ratios of SMA wire jackets has not previously been conducted. In this study, we investigate the effects of the stiffness and confinement ratios of steel jackets, and then compare the results with those of SMA wire jackets. In general, the stiffness ratios of SMA wire jackets are relatively smaller than those of steel jackets, and most of them have lower stiffness ratios because the Young's moduli of the SMAs are relatively small. The active confining pressure of the SMA wires does not improve the lower stiffness-ratio effect since the amount of active confining pressure is not sufficiently large.
Conformational Analysis of Stiff Chiral Polymers with End-Constraints
Kim, Jin Seob; Chirikjian, Gregory S.
2010-01-01
We present a Lie-group-theoretic method for the kinematic and dynamic analysis of chiral semi-flexible polymers with end constraints. The first is to determine the minimum energy conformations of semi-flexible polymers with end constraints, and the second is to perform normal mode analysis based on the determined minimum energy conformations. In this paper, we use concepts from the theory of Lie groups and principles of variational calculus to model such polymers as inextensible or extensible chiral elastic rods with coupling between twisting and bending stiffnesses, and/or between twisting and extension stiffnesses. This method is general enough to include any stiffness and chirality parameters in the context of elastic filament models with the quadratic elastic potential energy function. As an application of this formulation, the analysis of DNA conformations is discussed. We demonstrate our method with examples of DNA conformations in which topological properties such as writhe, twist, and linking number are calculated from the results of the proposed method. Given these minimum energy conformations, we describe how to perform the normal mode analysis. The results presented here build both on recent experimental work in which DNA mechanical properties have been measured, and theoretical work in which the mechanics of non-chiral elastic rods has been studied. PMID:20198114
NASA Astrophysics Data System (ADS)
Bianucci, Marco
2015-05-01
In this paper using a projection approach and defining the adjoint-Lie time evolution of differential operators, that generalizes the ordinary time evolution of functions, we obtain a Fokker-Planck equation for the distribution function of a part of interest of a large class of dynamical systems. The main assumptions are the weak interaction between the part of interest and the rest of the system (typically non linear) and the average linear response to external perturbations of the irrelevant part. We do not use ad hoc statistical assumptions to introduce as given a priori phenomenological equilibrium or transport coefficients. The drift terms induced by the interaction with the irrelevant part is obtained with a procedure that is reminiscent of that developed some years ago by Bianucci and Grigolini (see for example (Bianucci et al 1995 Phys. Rev. E 51 3002)) to derive in a ‘genuine’ way thermodynamics and statistical mechanics of macroscopic variables of interest starting from microscopic dynamics. However here we stay in a more broad and formal context where the system of interest could be dissipative and the interaction between the two systems could be non Hamiltonian, thus the approach of the cited paper can not be used to obtain the diffusion part of the Fokker-Planck equation. To face the problem of dealing with the series of differential operators stemming from the projection approach applied to this general case, we introduce the formalism of the Lie derivative and the corresponding adjoint-Lie time evolution of differential operators. In this theoretical framework we are able to obtain well defined analytic functions both for the drift and the diffusion coefficients of the Fokker-Planck equation. We think that the basic elements of Lie algebra introduced in our projection approach can be useful to achieve even more general and more formally elegant results than those here presented. Thus we consider this paper as a first step of this formal path to statistical mechanics of complex systems.
A stiffness probe based on force and vision sensing for soft tissue diagnosis.
Li, Jichun; Liu, Hongbin; Althoefer, Kaspar; Seneviratne, Lakmal D
2012-01-01
this paper introduces a novel approach of stiffness measurement based on force and vision sensing for tissue diagnosis. The developed probe is mainly composed of a force sensor and an image acquisition unit capable of obtaining contact area of probe-soft tissue interaction. By measuring the change of diameter of contact area during indentation test, the indentation depth can be determined. The stiffness of target soft tissue then can be evaluated by measuring indentation force and depth simultaneously. The probe can generalize a mechanical image to visualize the stiffness distribution for localization of abnormalities when sliding over soft tissue. The performance of the developed probe was validated by experiments on multiple materials including silicone phantoms and pork organs. The results show that the probe can perform stiffness measurement effectively when the probe indents or slides on the tissue surface. PMID:23366049
Experimental exposure to diesel exhaust increases arterial stiffness in man
Lundbck, Magnus; Mills, Nicholas L; Lucking, Andrew; Barath, Stefan; Donaldson, Ken; Newby, David E; Sandstrm, Thomas; Blomberg, Anders
2009-01-01
Introduction Exposure to air pollution is associated with increased cardiovascular morbidity, although the underlying mechanisms are unclear. Vascular dysfunction reduces arterial compliance and increases central arterial pressure and left ventricular after-load. We determined the effect of diesel exhaust exposure on arterial compliance using a validated non-invasive measure of arterial stiffness. Methods In a double-blind randomized fashion, 12 healthy volunteers were exposed to diesel exhaust (approximately 350 ?g/m3) or filtered air for one hour during moderate exercise. Arterial stiffness was measured using applanation tonometry at the radial artery for pulse wave analysis (PWA), as well as at the femoral and carotid arteries for pulse wave velocity (PWV). PWA was performed 10, 20 and 30 min, and carotid-femoral PWV 40 min, post-exposure. Augmentation pressure (AP), augmentation index (AIx) and time to wave reflection (Tr) were calculated. Results Blood pressure, AP and AIx were generally low reflecting compliant arteries. In comparison to filtered air, diesel exhaust exposure induced an increase in AP of 2.5 mmHg (p = 0.02) and in AIx of 7.8% (p = 0.01), along with a 16 ms reduction in Tr (p = 0.03), 10 minutes post-exposure. Conclusion Acute exposure to diesel exhaust is associated with an immediate and transient increase in arterial stiffness. This may, in part, explain the increased risk for cardiovascular disease associated with air pollution exposure. If our findings are confirmed in larger cohorts of susceptible populations, this simple non-invasive method of assessing arterial stiffness may become a useful technique in measuring the impact of real world exposures to combustion derived-air pollution. PMID:19284640
A unit-cell model of textile composite beams for predicting stiffness properties
NASA Technical Reports Server (NTRS)
Sankar, Bhavani V.; Marrey, Ramesh V.
1993-01-01
Flexural stiffness properties of a textile composite beam are obtained from a finite-element model of the unit cell. Three linearly independent deformations, namely, pure extension, pure bending and pure shear, are applied to the unit cell. The top and bottom surfaces of the beam are assumed to be traction free. Periodic boundary conditions on the lateral boundaries of the unit cell are enforced by multi-point constraint elements. From the forces acting on the unit cell, the flexural stiffness coefficients of the composite beam are obtained. The difficulties in determining the transverse shear stiffness are discussed, and a modified approach is presented. The methods are first verified by applying them to isotropic and bimaterial beams for which the results are known, and then illustrated for a simple plain-weave textile composite.
Design of a variable-stiffness robotic hand using pneumatic soft rubber actuators
NASA Astrophysics Data System (ADS)
Nagase, Jun-ya; Wakimoto, Shuichi; Satoh, Toshiyuki; Saga, Norihiko; Suzumori, Koichi
2011-10-01
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.
Factor Scores, Structure Coefficients, and Communality Coefficients
ERIC Educational Resources Information Center
Goodwyn, Fara
2012-01-01
This paper presents heuristic explanations of factor scores, structure coefficients, and communality coefficients. Common misconceptions regarding these topics are clarified. In addition, (a) the regression (b) Bartlett, (c) Anderson-Rubin, and (d) Thompson methods for calculating factor scores are reviewed. Syntax necessary to execute all four
Hyper-damping properties of a stiff and stable linear oscillator with a negative stiffness element
NASA Astrophysics Data System (ADS)
Antoniadis, I.; Chronopoulos, D.; Spitas, V.; Koulocheris, D.
2015-06-01
A simple, stiff, statically and dynamically stable linear oscillator incorporating a negative stiffness element is used as a template to provide a generic theoretical basis for a novel vibration damping and isolation concept. This oscillator is designed to present the same overall static stiffness, the same mass and to use the same damping element as a reference classical linear SDoF oscillator. Thus, no increase of the structure mass or the viscous damping is needed, as in the case of a traditional linear isolator, no decrease of the overall structure stiffness is required as in the case of 'zero-stiffness' oscillators with embedded negative stiffness elements. The difference from these two templates consists entirely in the proper redistribution and reallocation of the stiffness and the damping elements of the system. Once such an oscillator is optimally designed, it is shown to exhibit an extraordinary apparent damping ratio, which is even several orders of magnitude higher than that of the original SDoF system, especially in cases where the original damping of the SDoF system is extremely low. This extraordinary damping behavior is a result of the phase difference between the positive and the negative stiffness elastic forces, which is in turn a consequence of the proper redistribution of the stiffness and the damping elements. This fact ensures that an adequate level of elastic forces exists throughout the entire frequency range, able to counteract the inertial and the excitation forces. Consequently, a resonance phenomenon, which is inherent in the original linear SDoF system, cannot emerge in the proposed oscillator. The optimal parameter selection for the design of the negative stiffness oscillator is discussed. To further exhibit the advantages that such a design can generate, the suggested oscillator is implemented within a periodic acoustic metamaterial structure, inducing a radical increase in the damping of the propagating acoustic waves. The concept may find numerous technological applications, either as traditional vibration isolators or within advanced composite materials and metamaterials.
Nanoscale directional motion towards regions of stiffness.
Chang, Tienchong; Zhang, Hongwei; Guo, Zhengrong; Guo, Xingming; Gao, Huajian
2015-01-01
How to induce nanoscale directional motion via some intrinsic mechanisms pertaining to a nanosystem remains a challenge in nanotechnology. Here we show via molecular dynamics simulations that there exists a fundamental driving force for a nanoscale object to move from a region of lower stiffness toward one of higher stiffness on a substrate. Such nanoscale directional motion is induced by the difference in effective van der Waals potential energy due to the variation in stiffness of the substrate; i.e., all other conditions being equal, a nanoscale object on a stiffer substrate has lower van der Waals potential energy. This fundamental law of nanoscale directional motion could lead to promising routes for nanoscale actuation and energy conversion. PMID:25615480
The compressive stiffness of human pediatric heads.
Loyd, Andre Matthew; Nightingale, Roger W; Luck, Jason F; Song, Yin; Fronheiser, Lucy; Cutcliffe, Hattie; Myers, Barry S; Dale Bass, Cameron R
2015-11-01
Head injury is a persistent and costly problem for both children and adults. Globally, approximately 10 million people are hospitalized each year for head injuries. Knowing the structural properties of the head is important for modeling the response of the head in impact, and for providing insights into mechanisms of head injury. Hence, the goal of this study was to measure the sub-injurious structural stiffness of whole pediatric heads. 12 cadaveric pediatric (20-week-gestation to 16 years old) heads were tested in a battery of viscoelastic compression tests. The heads were compressed in both the lateral and anterior-posterior directions to 5% of gauge length at normalized deformation rates of 0.0005/s, 0.01/s, 0.1/s, and 0.3/s. Because of the non-linear nature of the response, linear regression models were used to calculate toe region (<2.5%) and elastic region (>2.5%) stiffness separately so that meaningful comparisons could be made across rate, age, and direction. The results showed that age was the dominant factor in predicting the structural stiffness of the human head. A large and statistically significant increase in the stiffness of both the toe region and the elastic region was observed with increasing age (p<0.0001), but no significant difference was seen across direction or normalized deformation rate. The stiffness of the elastic region increased from as low as 5N/mm in the neonate to >4500N/mm in the 16 year old. The changes in stiffness with age may be attributed to the disappearance of soft sutures and the thickening of skull bones with age. PMID:26476760
Ultrasonic measurements of stiffness in thermal-mechanically fatigued IM7/5260 composites
Seale, M.D.; Madaras, E.I. )
1999-08-01
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.
Assessments of endothelial function and arterial stiffness are reproducible in patients with COPD
Rodriguez-Miguelez, Paula; Seigler, Nichole; Bass, Leon; Dillard, Thomas A; Harris, Ryan A
2015-01-01
Background Elevated cardiovascular disease risk is observed in patients with COPD. Non-invasive assessments of endothelial dysfunction and arterial stiffness have recently emerged to provide mechanistic insight into cardiovascular disease risk in COPD; however, the reproducibility of endothelial function and arterial stiffness has yet to be investigated in this patient population. Objectives This study sought to examine the within-day and between-day reproducibility of endothelial function and arterial stiffness in patients with COPD. Methods Baseline diameter, peak diameter, flow-mediated dilation, augmentation index, augmentation index at 75 beats per minute, and pulse wave velocity were assessed three times in 17 patients with COPD (six males, eleven females, age range 4775 years old; forced expiratory volume in 1 second =51.5% predicted). Session A and B were separated by 3 hours (within-day), whereas session C was conducted at least 7 days following session B (between-day). Reproducibility was assessed by: 1) paired t-tests, 2) coefficients of variation, 3) coefficients of variation prime, 4) intra-class correlation coefficient, 5) Pearsons correlations (r), and 6) BlandAltman plots. Five acceptable assessments were required to confirm reproducibility. Results Six out of six within-day criteria were met for endothelial function and arterial stiffness outcomes. Six out of six between-day criteria were met for baseline and peak diameter, augmentation index and pulse wave velocity, whereas five out of six criteria were met for flow-mediated dilation. Conclusion The present study provides evidence for within-day and between-day reproducibility of endothelial function and arterial stiffness in patients with COPD. PMID:26396509
Elastic stiffness of a Skyrmion crystal.
Nii, Y; Kikkawa, A; Taguchi, Y; Tokura, Y; Iwasa, Y
2014-12-31
We observe the elastic stiffness and ultrasonic absorption of a Skyrmion crystal in the chiral-lattice magnet MnSi. The Skyrmion crystal lattice exhibits a stiffness 3 orders of magnitude smaller than that of the atomic lattice of MnSi, being as soft as the flux line lattice in type-II superconductors. The observed anisotropic elastic responses are consistent with the cylindrical shape of the Skyrmion spin texture. Phenomenological analysis reveals that the spin-orbit coupling is responsible for the emergence of anisotropic elasticity in the Skyrmion lattice. PMID:25615379
The stiff shoulder; A case study.
Hall, Kevin; Mercer, Christopher
2015-12-01
Clinicians working in outpatient departments and advanced practitioner clinics frequently encounter patients presenting with multidirectional stiffness of the glenohumeral joint. This case report describes the assessment and treatment of a patient presenting with glenohumeral joint stiffness and describes the possible differential diagnoses. The evidence base used to inform the decision-making process is presented and the use of radiology that helped to ultimately establish the diagnosis is discussed. The clinical reasoning process of applying knowledge and experience to identify patient problems and to make appropriate decisions that result in positive patient outcomes is discussed. The case report highlights the importance of early diagnosis. PMID:26096901
Stiffness and strength of hierarchical polycrystalline materials with imperfect interfaces
NASA Astrophysics Data System (ADS)
Paggi, Marco; Wriggers, Peter
2012-04-01
In this study we investigate the effect of imperfect (not perfectly bonded) interfaces on the stiffness and strength of hierarchical polycrystalline materials. As a case study we consider a honeycomb cellular polycrystal used for drilling and cutting tools. The conclusions of the analysis are, however, general and applicable to any material with structural hierarchy. Regarding the stiffness, generalized expressions for the Voigt and Reuss estimates of the bounds to the effective elastic modulus of heterogeneous materials are derived. The generalizations regard two aspects that are not included in the standard Reuss and Voigt estimates. The first novelty consists in considering finite thickness interfaces between the constituents undergoing damage up to final debonding. The second generalization consists of interfaces not perpendicular or parallel to the loading direction, i.e., when isostress or isostrain conditions are not satisfied. In this case, approximate expressions for the effective elastic modulus are obtained by performing a computational homogenization approach. In the second part of the paper, the homogenized response of a representative volume element (RVE) of the honeycomb cellular polycrystalline material with one or two levels of hierarchy is numerically investigated. This is put forward by using the cohesive zone model (CZM) for finite thickness interfaces recently proposed by the authors and implemented in the finite element program FEAP. From tensile tests we find that the interface nonlinearity significantly contributes to the deformability of the material. Increasing the number of hierarchical levels, the deformability increases. The RVE is tested in two different directions and, due to different orientations of the interfaces and Mixed Mode deformation, anisotropy in stiffness and strength is observed. Stiffness anisotropy is amplified by increasing the number of hierarchical levels. Finally, the interaction between interfaces at different hierarchical levels is numerically characterized. A condition for scale separation, which corresponds to the independence of the material tensile strength from the properties of the interfaces in the second level, is established. When this condition is fulfilled, the material microstructure at the second level can be efficiently replaced by an effective homogeneous continuum with a homogenized stress-strain response. From the engineering point of view, the proposed criterion of scale separation suggests how to design the optimal microstructure of a hierarchical level to maximize the material tensile strength. An interpretation of this phenomenon according to the concept of flaw tolerance is finally presented.
Meta-Analysis of Coefficient Alpha
ERIC Educational Resources Information Center
Rodriguez, Michael C.; Maeda, Yukiko
2006-01-01
The meta-analysis of coefficient alpha across many studies is becoming more common in psychology by a methodology labeled reliability generalization. Existing reliability generalization studies have not used the sampling distribution of coefficient alpha for precision weighting and other common meta-analytic procedures. A framework is provided for
NASA Astrophysics Data System (ADS)
Yang, J.; Sun, S. S.; Du, H.; Li, W. H.; Alici, G.; Deng, H. X.
2014-10-01
Magneto-rheological elastomers (MREs) have attracted notable credits in the development of smart isolators and absorbers due to their controllable stiffness and damping properties. For the purpose of mitigating unwanted structural and/or machinery vibrations, the traditional MRE-based isolators have been generally proven effective because the MR effect can increase the stiffness when the magnetic field is strengthened. This study presents a novel MRE isolator that experienced reduced stiffness when the applied current was increased. This innovative work was accomplished by applying a hybrid magnet (electromagnet and permanent magnets) onto a multilayered MRE structure. To characterise this negative changing stiffness concept, a multilayered MRE isolator with a hybrid magnet was first designed, fabricated and then tested to measure its properties. An obvious reduction of the effective stiffness and natural frequency of the proposed MRE isolator occurred when the current was continuously adjusted. This device could also work as a conventional MRE isolator as its effective stiffness and natural frequency also increased when a negative current was applied. Further testing was carried out on a one-degree-of-freedom system to assess how effectively this device could isolate vibration. In this experiment, two cases were considered; in each case, the vibration of the primary system was obviously attenuated under ON-OFF control logic, thus demonstrating the feasibility of this novel design as an alternative adaptive vibration isolator.
Davis, J.L.; Grant, J.W.
2014-01-01
Anatomically correct turtle utricle geometry was incorporated into two finite element models. The geometrically accurate model included appropriately shaped macular surface and otoconial layer, compact gel and column filament (or shear) layer thicknesses and thickness distributions. The first model included a shear layer where the effects of hair bundle stiffness was included as part of the shear layer modulus. This solid models undamped natural frequency was matched to an experimentally measured value. This frequency match established a realistic value of the effective shear layer Youngs modulus of 16 Pascals. We feel this is the most accurate prediction of this shear layer modulus and fits with other estimates (Kondrachuk, 2001b). The second model incorporated only beam elements in the shear layer to represent hair cell bundle stiffness. The beam element stiffnesss were further distributed to represent their location on the neuroepithelial surface. Experimentally measured striola hair cell bundles mean stiffness values were used in the striolar region and the mean extrastriola hair cell bundles stiffness values were used in this region. The results from this second model indicated that hair cell bundle stiffness contributes approximately 40% to the overall stiffness of the shear layer hair cell bundle complex. This analysis shows that high mass saccules, in general, achieve high gain at the sacrifice of frequency bandwidth. We propose the mechanism by which this can be achieved is through increase the otoconial layer mass. The theoretical difference in gain (deflection per acceleration) is shown for saccules with large otoconial layer mass relative to saccules and utricles with small otoconial layer mass. Also discussed is the necessity of these high mass saccules to increase their overall system shear layer stiffness. Undamped natural frequencies and mode shapes for these sensors are shown. PMID:25445820
Comparison of surgical outcome in impingement syndrome with and without stiff shoulder
Park, Jin-Young; Pandher, Dilbans Singh; Moon, Gi-Hyuk; Yoo, Moon-Jib; Lee, Sung Tae
2008-01-01
Background: In impingment syndrome with associated stiff shoulder the general protocol of management is to conservatively treat the stiff shoulder followed by operative treatment of the impingement syndrome. This consecutive prospective study was carried out to evaluate the functional outcome of surgical management for impingement syndrome associated with stiff shoulder and to compare the results with surgical management of impingement syndrome alone. Materials and Methods: We evaluated a total of 100 patients with impingement syndrome, consisting of 76 patients with impingement syndrome alone (Group A) and 24 patients of stiff shoulder associated with impingement syndrome (Group B). Group A patients were treated by subacromial decompression alone and Group B patients were treated by closed manipulation under anesthesia followed by subacromial decompression. Results: According to the American Shoulder and Elbow Surgeons (ASES) evaluation score satisfactory results were obtained in 80% patients of Group A and 67% patients of Group B, while for patients with diabetes [(n = 18), Group A (n = 11), Group B (n = 7)] satisfactory results were achieved in 82% of patients of Group A(9/11) and 43% of Group B(3/7). Overall, Group B patients had a lower range of motion for external rotation postoperatively, thus indicating that procedures to improve the external rotation, such as a release of the rotator interval or anterior capsule, might be considered in conjunction with other surgical procedures in patients with impingement syndrome with associated stiffness to further improve functional outcome. Conclusion: Acromioplasty can be performed in stiff shoulder associated with impingement syndrome without fears of further worsening of stiffness from adhesions with the exposed raw undersurface of acromian. Patients with diabetes mellitus and shoulder stiffness tend to have poor clinical outcomes and must receive appropriate counseling preoperatively. PMID:19826525
Davis, J L; Grant, J W
2014-12-01
Anatomically correct turtle utricle geometry was incorporated into two finite element models. The geometrically accurate model included appropriately shaped macular surface and otoconial layer, compact gel and column filament (or shear) layer thicknesses and thickness distributions. The first model included a shear layer where the effects of hair bundle stiffness was included as part of the shear layer modulus. This solid model's undamped natural frequency was matched to an experimentally measured value. This frequency match established a realistic value of the effective shear layer Young's modulus of 16 Pa. We feel this is the most accurate prediction of this shear layer modulus and fits with other estimates (Kondrachuk, 2001b). The second model incorporated only beam elements in the shear layer to represent hair cell bundle stiffness. The beam element stiffness's were further distributed to represent their location on the neuroepithelial surface. Experimentally measured striola hair cell bundles mean stiffness values were used in the striolar region and the mean extrastriola hair cell bundles stiffness values were used in this region. The results from this second model indicated that hair cell bundle stiffness contributes approximately 40% to the overall stiffness of the shear layer-hair cell bundle complex. This analysis shows that high mass saccules, in general, achieve high gain at the sacrifice of frequency bandwidth. We propose the mechanism by which this can be achieved is through increase the otoconial layer mass. The theoretical difference in gain (deflection per acceleration) is shown for saccules with large otoconial layer mass relative to saccules and utricles with small otoconial layer mass. Also discussed is the necessity of these high mass saccules to increase their overall system shear layer stiffness. Undamped natural frequencies and mode shapes for these sensors are shown. PMID:25445820
Nonlinear stiffness characteristics of the annular ligament.
Lauxmann, M; Eiber, A; Haag, F; Ihrle, S
2014-10-01
The annular ligament provides a compliant connection of the stapes to the oval window. To estimate the stiffness characteristics of the annular ligament, human temporal bone measurements were conducted. A force was applied sequentially at several points on the stapes footplate leading to different patterns of displacement with different amounts of translational and rotational components. The spatial displacement of the stapes footplate was measured using a laser vibrometer. The experiments were performed on several stapes with dissected chain and the force was increased stepwise, resulting in load-deflection curves for each force application point. The annular ligament exhibited a progressive stiffening characteristic in combination with an inhomogeneous stiffness distribution. When a centric force, orientated in the lateral direction, was applied to the stapes footplate, the stapes head moved laterally and in the posterior-inferior direction. Based on the load-deflection curves, a mechanical model of the annular ligament was derived. The mathematical representation of the compliance of the annular ligament results in a stiffness matrix with a nonlinear dependence on stapes displacement. This description of the nonlinear stiffness allows simulations of the sound transfer behavior of the middle ear for different preloads. PMID:25324078
Frequency-Dependent Fracture Specific Stiffness
NASA Astrophysics Data System (ADS)
Pyrak-Nolte, L. J.; Folz, M. A.; Acosta-Colon, A.
2003-12-01
Monitoring the hydraulic properties of fractures remotely through their seismic signatures is an important goal for field hydrology. Empirical studies have shown that the hydraulic properties of a fracture are implicitly related to the fracture specific stiffness through the amount and distribution of contact area and apertures that arise from two rough surfaces in contact. Complicating this simple picture are seismic measurements that indicate frequency-dependent stiffness, i.e., a scale-dependent fracture stiffness where the scale is set by the wavelength. Thus relating the hydraulic properties of fractures to seismic measurements becomes a scale dependent problem. We have performed laboratory experiments to examine the phenomenon of frequency dependent fracture specific stiffness to aid in the assessment of the hydraulic properties of a fracture using seismic techniques. To this end, we have developed a photolithographic technique with which we can construct synthetic fractures of known fracture geometry with feature sizes controlled over several orders of magnitude. The synthetic fracture (and the control non-fractured samples) are made from acrylic cylinders that measure 15.0 cm in diameter by 7.7 cm in height. The diameter of the samples enables us to sample the acoustic properties of the fracture using acoustic lens over regions that range in scale from 10 mm to 60 mm. A confinement cell controls the normal stress on the fracture. Seismic measurements were made with broadband compressional-mode piezoelectric transducers enabling one-order of magnitude in frequency. We found that when the wavelength is smaller than the asperity size, a linear dependence of fracture specific stiffness on frequency occurs. In this geometric ray regime the asymptotic value of the transmission function provides a direct measure of the contact area of the fracture. On the other hand, when the asperity spacing is less than an eighth of a wavelength, the fracture behaves as a displacement discontinuity and exhibits a frequency-independent fracture specific stiffness. For intermediate asperity spacings, mixed behavior (that may include resonant scattering) was observed. By understanding how to interpret fracture specific stiffness as a function of frequency, we seek to develop a better interpretation of the hydraulic properties of fractures based on seismic measurements. Acknowledgments: The Authors acknowledge support of this research by the Geosciences Research Program, Office of Basic Energy Sciences, US Department of Energy. LJPN wishes to acknowledge Purdue University Faculty Scholar
Precise damping and stiffness extraction in acoustic driven cantilever in liquid
NASA Astrophysics Data System (ADS)
Maali, Abdelhamid; Boisgard, Rodolphe
2013-10-01
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.
NASA Technical Reports Server (NTRS)
Majda, George
1986-01-01
One-leg and multistep discretizations of variable-coefficient linear systems of ODEs having both slow and fast time scales are investigated analytically. The stability properties of these discretizations are obtained independent of ODE stiffness and compared. The results of numerical computations are presented in tables, and it is shown that for large step sizes the stability of one-leg methods is better than that of the corresponding linear multistep methods.
Shah, S. N. R.; Sulong, N. H. Ramli; Shariati, Mahdi; Jumaat, M. Z.
2015-01-01
Steel pallet rack (SPR) beam-to-column connections (BCCs) are largely responsible to avoid the sway failure of frames in the down-aisle direction. The overall geometry of beam end connectors commercially used in SPR BCCs is different and does not allow a generalized analytic approach for all types of beam end connectors; however, identifying the effects of the configuration, profile and sizes of the connection components could be the suitable approach for the practical design engineers in order to predict the generalized behavior of any SPR BCC. This paper describes the experimental behavior of SPR BCCs tested using a double cantilever test set-up. Eight sets of specimens were identified based on the variation in column thickness, beam depth and number of tabs in the beam end connector in order to investigate the most influential factors affecting the connection performance. Four tests were repeatedly performed for each set to bring uniformity to the results taking the total number of tests to thirty-two. The moment-rotation (M-?) behavior, load-strain relationship, major failure modes and the influence of selected parameters on connection performance were investigated. A comparative study to calculate the connection stiffness was carried out using the initial stiffness method, the slope to half-ultimate moment method and the equal area method. In order to find out the more appropriate method, the mean stiffness of all the tested connections and the variance in values of mean stiffness according to all three methods were calculated. The calculation of connection stiffness by means of the initial stiffness method is considered to overestimate the values when compared to the other two methods. The equal area method provided more consistent values of stiffness and lowest variance in the data set as compared to the other two methods. PMID:26452047
Shah, S N R; Sulong, N H Ramli; Shariati, Mahdi; Jumaat, M Z
2015-01-01
Steel pallet rack (SPR) beam-to-column connections (BCCs) are largely responsible to avoid the sway failure of frames in the down-aisle direction. The overall geometry of beam end connectors commercially used in SPR BCCs is different and does not allow a generalized analytic approach for all types of beam end connectors; however, identifying the effects of the configuration, profile and sizes of the connection components could be the suitable approach for the practical design engineers in order to predict the generalized behavior of any SPR BCC. This paper describes the experimental behavior of SPR BCCs tested using a double cantilever test set-up. Eight sets of specimens were identified based on the variation in column thickness, beam depth and number of tabs in the beam end connector in order to investigate the most influential factors affecting the connection performance. Four tests were repeatedly performed for each set to bring uniformity to the results taking the total number of tests to thirty-two. The moment-rotation (M-?) behavior, load-strain relationship, major failure modes and the influence of selected parameters on connection performance were investigated. A comparative study to calculate the connection stiffness was carried out using the initial stiffness method, the slope to half-ultimate moment method and the equal area method. In order to find out the more appropriate method, the mean stiffness of all the tested connections and the variance in values of mean stiffness according to all three methods were calculated. The calculation of connection stiffness by means of the initial stiffness method is considered to overestimate the values when compared to the other two methods. The equal area method provided more consistent values of stiffness and lowest variance in the data set as compared to the other two methods. PMID:26452047
The impact of the type of derotation mechanism on the stiffness of the Ilizarov fixator.
Morasiewicz, Piotr; Filipiak, Jaros?aw; Konietzko, Marcin; Dragan, Szymon
2012-01-01
One of the applications of the Ilizarov apparatus is the correction of rotational deformities. There are several types of designs commonly used for derotation. Different types of derotators have different mechanical properties, which affect the stability of the entire Ilizarov apparatus. The aim of this study was to determine the stiffness of the Ilizarov fixator depending on the type of derotation mechanism. We analyse three types of derotators: the type Z, the type H, and the cubicoid derotator. The tests were conducted on physical models in which the fixator analysed was fitted to polyethylene pipe segments. The reference fixator was the Ilizarov apparatus in the configuration adapted for thigh lengthening. The pipe segments intersected at a point corresponding to the osteotomy site of the distal thigh. The fixator was assembled with one proximal arch fixed with two Schanz screws, a proximal ring fixed with two Kirschner wires (K-wires), a middle free ring, and a distal ring fixed with three K-wires. There were three different types of derotation mechanisms installed between the proximal and middle rings. We determined the axial stiffness kA and the transverse stiffnesses of the compared fixators in two planes: frontal kM-L and sagittal kA-P. The results of the research lead to two basic conclusions. Firstly, the use of any of the derotators analysed has no negative impact on the stiffness of the Ilizarov apparatus. Secondly, similar stiffness values of the fixators with different derotation mechanisms suggest their equal applicability and the choice between them can be made based on practical considerations. In the case of axial stiffness, the differences do not exceed 7.5%. The highest value of stiffness kA was obtained for the type H derotator, while the lowest value was obtained for the type Z derotator. There is a greater difference in the case of transverse stiffness in the sagittal plane, which only concerns the fixator with the type Z derotators. The stiffness coefficient kA-P for that fixator is lower by approximately 19% compared to the reference fixator. PMID:22742714
Global stiffness of hex-can assembly in a uniform force field. [LMFBR
Ju, F.D.; Bennett, J.
1980-07-01
Two approximate constitutive equations are derived that can be used to represent the global stiffness of a hexagonal cross-section duct in a uniform force field. The first equation uses a single coefficient that can be determined from Poisson's ratio for the material and the duct geometry. This equation is useful for isothermal applications. The second equation can be used to account for temperature-varying material properties and requires that two coefficients be determined from Poisson's ratio and the duct geometry. These equations are useful both in reactor safety analysis and design.
Tsagarikis, Nikos G; Jafari, Amir; Caldwell, Darwin G
2010-01-01
The design of robots required to work in the close vicinity or physically interact with humans such as humanoids machines, rehabilitation or human performance augmentation systems should not follow the traditional design rule 'stiffer is better'. Safety is a particularly vital concern in these systems and to maximize it a different design approach should be used. The role of compliance in improving specific suspects of the robotic system, including safety and energy efficiency, has been studied and validated in many works. This work presents the design and realization of a new variable compliance actuator for robots physically interacting with humans, e.g. prosthesis devices and exoskeleton augmentation systems. The actuator can independently control the equilibrium position and stiffness using two motors. The main novelty of the proposed variable stiffness actuator is that the stiffness regulation is achieved not through the pretension of the elastic elements which needs the stiffness tuning actuator to act against the forces generated by the springs but by mechanically adjusting the fixation of the spring elements. As a result the stiffness actuator does not need to act against the spring forces reducing the energy required for the stiffness adjustment to minimal. PMID:21095917
Airfoil design: Finding the balance between design lift and structural stiffness
NASA Astrophysics Data System (ADS)
Bak, Christian; Gaudern, Nicholas; Zahle, Frederik; Vronsky, Tomas
2014-06-01
When upscaling wind turbine blades there is an increasing need for high levels of structural efficiency. In this paper the relationships between the aerodynamic characteristics; design lift and lift-drag ratio; and the structural characteristics were investigated. Using a unified optimization setup, airfoils were designed with relative thicknesses between 18% and 36%, a structural box height of 85% of the relative thickness, and varying box widths in chordwise direction between 20% and 40% of the chord length. The results from these airfoil designs showed that for a given flapwise stiffness, the design lift coefficient increases if the box length reduces and at the same time the relative thickness increases. Even though the conclusions are specific to the airfoil design approach used, the study indicated that an increased design lift required slightly higher relative thickness compared to airfoils with lower design lift to maintain the flapwise stiffness. Also, the study indicated that the lift-drag ratio as a function of flapwise stiffness was relatively independent of the airfoil design with a tendency that the lift-drag ratio decreased for large box lengths. The above conclusions were supported by an analysis of the three airfoil families Riso-C2, DU and FFA, where the lift-drag ratio as a function of flapwise stiffness was decreasing, but relatively independent of the airfoil design, and the design lift coefficient was varying depending on the design philosophy. To make the analysis complete also design lift and lift- drag ratio as a function of edgewise and torsional stiffness were shown.
Aortic stiffness: pathophysiology, clinical implications, and approach to treatment
Sethi, Salil; Rivera, Oscar; Oliveros, Rene; Chilton, Robert
2014-01-01
Aortic stiffness is a hallmark of aging, and classic cardiovascular risk factors play a role in accelerating this process. Current changes in medicine, which focus on preventive care, have led to a growing interest in noninvasive evaluation of aortic stiffness. Aortic stiffness has emerged as a good tool for further risk stratification because it has been linked to increased risk of atherosclerotic heart disease, myocardial infarction, heart failure, and stroke. This has led to the invention and validation of multiple methods to measure aortic stiffness. Pulse wave velocity is emerging as the gold standard for evaluation of aortic stiffness. This review focuses on the pathophysiology involved in aortic stiffness, methods available for evaluation of aortic stiffness, the importance of central pressure as a predictor of future cardiovascular events, and therapies that affect aortic stiffness. PMID:24910511
Lamb Wave Stiffness Characterization of Composites Undergoing Thermal-Mechanical Aging
NASA Technical Reports Server (NTRS)
Seale, Michael D.; Madaras, Eric I.
2004-01-01
The introduction of new, advanced composite materials into aviation systems requires a thorough understanding of the long term effects of combined thermal and mechanical loading upon those materials. Analytical methods investigating the effects of intense thermal heating combined with mechanical loading have been investigated. The damage mechanisms and fatigue lives were dependent on test parameters as well as stress levels. Castelli, et al. identified matrix dominated failure modes for out-of-phase cycling and fiber dominated damage modes for in-phase cycling. In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. To help evaluate the effect of aging, a suitably designed Lamb wave measurement system is being used to obtain bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system works by exciting an antisymmetric Lamb wave and calculating the velocity at each frequency from the known transducer separation and the measured time-of-flight. The same peak in the waveforms received at various distances is used to measure the time difference between the signals. The velocity measurements are accurate and repeatable to within 1% resulting in reconstructed stiffness values repeatable to within 4%. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. A mechanical scanner is used to move the sensors over the surface to map the time-of-flight, velocity, or stiffnesses of the entire specimen. Access to only one side of the material is required and no immersion or couplants are required because the sensors are dry coupled to the surface of the plate. In this study, the elastic stiffnesses D(sub 11), D(sub 22), A(sub 44), and A(sub 55) as well as time-of-flight measurements for composite samples that have undergone combined thermal and mechanical aging for a duration of 10,000 hours are reported.
NASA Astrophysics Data System (ADS)
Jiang, Yao; Li, Tie-Min; Wang, Li-Ping
2015-09-01
This paper investigates the stiffness modeling of compliant parallel mechanism (CPM) based on the matrix method. First, the general compliance matrix of a serial flexure chain is derived. The stiffness modeling of CPMs is next discussed in detail, considering the relative positions of the applied load and the selected displacement output point. The derived stiffness models have simple and explicit forms, and the input, output, and coupling stiffness matrices of the CPM can easily be obtained. The proposed analytical model is applied to the stiffness modeling and performance analysis of an XY parallel compliant stage with input and output decoupling characteristics. Then, the key geometrical parameters of the stage are optimized to obtain the minimum input decoupling degree. Finally, a prototype of the compliant stage is developed and its input axial stiffness, coupling characteristics, positioning resolution, and circular contouring performance are tested. The results demonstrate the excellent performance of the compliant stage and verify the effectiveness of the proposed theoretical model. The general stiffness models provided in this paper will be helpful for performance analysis, especially in determining coupling characteristics, and the structure optimization of the CPM.
Jiang, Yao; Li, Tie-Min; Wang, Li-Ping
2015-09-01
This paper investigates the stiffness modeling of compliant parallel mechanism (CPM) based on the matrix method. First, the general compliance matrix of a serial flexure chain is derived. The stiffness modeling of CPMs is next discussed in detail, considering the relative positions of the applied load and the selected displacement output point. The derived stiffness models have simple and explicit forms, and the input, output, and coupling stiffness matrices of the CPM can easily be obtained. The proposed analytical model is applied to the stiffness modeling and performance analysis of an XY parallel compliant stage with input and output decoupling characteristics. Then, the key geometrical parameters of the stage are optimized to obtain the minimum input decoupling degree. Finally, a prototype of the compliant stage is developed and its input axial stiffness, coupling characteristics, positioning resolution, and circular contouring performance are tested. The results demonstrate the excellent performance of the compliant stage and verify the effectiveness of the proposed theoretical model. The general stiffness models provided in this paper will be helpful for performance analysis, especially in determining coupling characteristics, and the structure optimization of the CPM. PMID:26429482
Light weight high-stiffness stage platen
Spence, Paul A. (Pleasanton, CA)
2001-01-01
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.
Microfinish As A Function Of Machine Stiffness
NASA Astrophysics Data System (ADS)
Watt, Gordon J.
1987-01-01
Stiffness of a machine must be known between the tip of the cutting tool and the surface being machined in order to correlate with microfinish. Signature of the machine tool and its environs are registered on the micro-machined surface. Imperfections are triggered by disturbances which may originate off the machine, from the machine, or by reaction between the tool and the workpiece. The machine transfer function is a complex mechanical system with many input points and resonance frequencies to be contended with. This paper deals with recognizable surface imperfections which are related back to mechanical parameters in and between the machine elements. To be complete, one must include spindles, slides, supports, vibration isolators, tool holders, tools, fixtures, and the workpiece itself. Their relation to sources of disturbance is discussed and examples are given of surface measurements made which identify the relation between machine stiffness and microfinish signatures.
Stiffness and mass matrices for shells of revolution (SAMMSOR II)
NASA Technical Reports Server (NTRS)
Tillerson, J. R.; Haisler, W. E.
1974-01-01
Utilizing element properties, structural stiffness and mass matrices are generated for as many as twenty harmonics and stored on magnetic tape. Matrices generated constitute input data to be used by other stiffness of revolution programs. Variety of boundary and loading conditions can be employed without having to create new mass and stiffness matrices for each case.
Stiff modes in spinvalve simulations with OOMMF
NASA Astrophysics Data System (ADS)
Mitropoulos, Spyridon; Tsiantos, Vassilis; Ovaliadis, Kyriakos; Kechrakos, Dimitris; Donahue, Michael
2016-04-01
Micromagnetic simulations are an important tool for the investigation of magnetic materials. Micromagnetic software uses various techniques to solve differential equations, partial or ordinary, involved in the dynamic simulations. Euler, Runge-Kutta, Adams, and BDF (Backward Differentiation Formulae) are some of the methods used for this purpose. In this paper, spinvalve simulations are investigated. Evidence is presented showing that these systems have stiff modes, and that implicit methods such as BDF are more effective than explicit methods in such cases.
Circulating adhesion molecules and arterial stiffness
Dogu Kilic, Ismail; Alihanoglu, Yusuf I; Yildiz, Bekir Serhat; Evrengul, Harun; Findikoglu, Gulin; Uslu, Sukriye; Rota, Simin
2015-01-01
Summary Aim VCAM-1 and ICAM-1 are two important members of the immunoglobulin gene superfamily of adhesion molecules, and their potential role as biomarkers of diagnosis, severity and prognosis of cardiovascular disease has been investigated in a number of clinical studies. The aim of the present study was to determine the relationship between circulating ICAM-1 and VCAM-1 levels and aortic stiffness in patients referred for echocardiographic examination. Methods Aortic distensibility was determined by echocardiography using systolic and diastolic aortic diameters in 63 consecutive patients referred for echocardiography. Venous samples were collected in the morning after a 12-hour overnight fast, and serum concentrations of ICAM-1 and VCAM-1 were measured using commercial enzyme immunoassay kits. Results Data of a total of 63 participants (mean age 55.6 10.5 years, 31 male) were included in the study. Circulating levels of adhesion molecules were VCAM-1: 12.604 3.904 ng/ml and ICAM-1: 45.417 31.429 ng/ml. We were unable to demonstrate any correlation between indices of aortic stiffness and VCAM-1 and ICAM-1 levels. Conclusion The role of soluble adhesion molecules in cardiovascular disease has not been fully established and clinical studies show inconsistent results. Our results indicate that levels of circulating adhesion molecules cannot be used as markers of aortic stiffness in patients. PMID:25784313
Aortic stiffness in normal and hypertensive pregnancy.
Avni, B; Frenkel, G; Shahar, L; Golik, A; Sherman, D; Dishy, V
2010-02-01
The objective of this study was to examine whether aortic stiffness, as assessed by pulse wave analysis, could reliably discriminate between normal and hypertensive pregnancies. One hundred pregnant women were studied: five with severe pre-eclampsia, 27 with gestational hypertension, 14 with chronic hypertension and 54 with normal pregnancy. Central hemodynamic parameters were obtained by an applanation tonometry and included central aortic systolic blood pressure (CSBP), central aortic diastolic blood pressure (CDBP), augmentation pressure (AP), augmentation index (AIx), AIx corrected to a heart rate of 75 (AIx@75) and time to reflection (Tr). All measures of aortic stiffness, including AP, AIx and AIx@75 were significantly higher in women with gestational hypertension and pre-eclampsia compared with normal pregnancies and women with chronic hypertension (p < 0.05 for all comparisons). There were no significant differences between normal pregnancies and women with chronic hypertension (p > 0.05 for all comparisons). Tr was significantly shorter in women with pre-eclampsia and gestational hypertension compared with normal pregnancies (p < 0.05). Aortic stiffness, as assessed by pulse wave analysis, is significantly increased in women with pre-eclampsia and gestational hypertension but not in treated women with chronic hypertension. Pulse wave analysis has a potential as a screening tool in women at high risk for pre-eclampsia. The final role of this method should be determined in prospective studies. PMID:20001391
Fyhrie, D P; Vashishth, D
2000-02-01
The yield strength and ultimate strength of cortical and cancellous bone tissue are very highly correlated to bone stiffness. For samples of human vertebral cancellous bone in compression and for bovine cortical bone in tension, the coefficient of determination (r2) for regression between ultimate strength and stiffness was 0.89 and 0.92, and between yield strength and stiffness it was 0.94 and 0.93, respectively. The slope of the regression for human vertebral cancellous bone ultimate strength predicted by stiffness was not statistically different from similar regressions for cortical bone in tension in either a bovine sample or in published data from multiple species. We believe that the observed correlation results from the evolutionary need to build sufficiently strong bones using cells that are sensitive to deformation and that directly control bone stiffness, but not strength. The practical significance of this work is that an in vivo estimate of bone stiffness (e.g., from ultrasound measurement) may be a surrogate for bone strength. PMID:10678412
Yin, Meng; Kolipaka, Arunark; Woodrum, David A.; Glaser, Kevin J.; Romano, Anthony J; Manduca, Armando; Talwalkar, Jayant A.; Araoz, Philip A.; McGee, Kiaran P.; Anavekar, Nandan S.; Ehman, Richard L.
2013-01-01
Purpose To investigate the influence of portal pressure on the shear stiffness of the liver and spleen in a well-controlled in vivo porcine model with MR Elastography (MRE). A significant correlation between portal pressure and tissue stiffness could be used to noninvasively assess increased portal venous pressure (portal hypertension), which is a frequent clinical condition caused by cirrhosis of the liver and is responsible for the development of many lethal complications. Materials and Methods During multiple intra-arterial infusions of Dextran-40 in three adult domestic pigs in vivo, 3-D abdominal MRE was performed with left ventricle and portal catheters measuring blood pressure simultaneously. Least-squares linear regressions were used to analyze the relationship between tissue stiffness and portal pressure. Results Liver and spleen stiffness have a dynamic component that increases significantly following an increase in portal or left ventricular pressure. Correlation coefficients with the linear regressions between stiffness and pressure exceeded 0.8 in most cases. Conclusion The observed stiffness-pressure relationship of the liver and spleen could provide a promising noninvasive method for assessing portal pressure. Using MRE to study the tissue mechanics associated with portal pressure may provide new insights into the natural history and pathophysiology of hepatic diseases and may have significant diagnostic value in the future. PMID:23418135
Strong and stiff aramid nanofiber/carbon nanotube nanocomposites.
Zhu, Jiaqi; Cao, Wenxin; Yue, Mingli; Hou, Ying; Han, Jiecai; Yang, Ming
2015-03-24
Small but strong carbon nanotubes (CNTs) are fillers of choice for composite reinforcement owing to their extraordinary modulus and strength. However, the mechanical properties of the nanocomposites are still much below those for mechanical parameters of individual nanotubes. The gap between the expectation and experimental results arises not only from imperfect dispersion and poor load transfer but also from the unavailability of strong polymers that can be effectively utilized within the composites of nanotubes. Aramid nanofibers (ANFs) with analogous morphological features to nanotubes represent a potential choice to complement nanotubes given their intrinsic high mechanical performance and the dispersible nature, which enables solvent-based processing methods. In this work, we showed that composite films made from ANFs and multiwalled CNTs (MWCNTs) by vacuum-assisted flocculation and vacuum-assisted layer-by-layer assembly exhibited high ultimate strength of up to 383 MPa and Young's modulus (stiffness) of up to 35 GPa, which represent the highest values among all the reported random CNT nanocomposites. Detailed studies using different imaging and spectroscopic characterizations suggested that the multiple interfacial interactions between nanotubes and ANFs including hydrogen bonding and π-π stacking are likely the key parameters responsible for the observed mechanical improvement. Importantly, our studies further revealed the attractive thermomechanical characteristics of these nanocomposites with high thermal stability (up to 520 °C) and ultralow coefficients of thermal expansion (2-6 ppm·K(-1)). Our results indicated that ANFs are promising nanoscale building blocks for functional ultrastrong and stiff materials potentially extendable to nanocomposites based on other nanoscale fillers. PMID:25712334
Estimation of Quasi-Stiffness of the Human Hip in the Stance Phase of Walking
Shamaei, Kamran; Sawicki, Gregory S.; Dollar, Aaron M.
2013-01-01
This work presents a framework for selection of subject-specific quasi-stiffness of hip orthoses and exoskeletons, and other devices that are intended to emulate the biological performance of this joint during walking. The hip joint exhibits linear moment-angular excursion behavior in both the extension and flexion stages of the resilient loading-unloading phase that consists of terminal stance and initial swing phases. Here, we establish statistical models that can closely estimate the slope of linear fits to the moment-angle graph of the hip in this phase, termed as the quasi-stiffness of the hip. Employing an inverse dynamics analysis, we identify a series of parameters that can capture the nearly linear hip quasi-stiffnesses in the resilient loading phase. We then employ regression analysis on experimental moment-angle data of 216 gait trials across 26 human adults walking over a wide range of gait speeds (0.75–2.63 m/s) to obtain a set of general-form statistical models that estimate the hip quasi-stiffnesses using body weight and height, gait speed, and hip excursion. We show that the general-form models can closely estimate the hip quasi-stiffness in the extension (R2 = 92%) and flexion portions (R2 = 89%) of the resilient loading phase of the gait. We further simplify the general-form models and present a set of stature-based models that can estimate the hip quasi-stiffness for the preferred gait speed using only body weight and height with an average error of 27% for the extension stage and 37% for the flexion stage. PMID:24349136
Damage detection on sudden stiffness reduction based on discrete wavelet transform.
Chen, Bo; Chen, Zhi-wei; Wang, Gan-jun; Xie, Wei-ping
2014-01-01
The sudden stiffness reduction in a structure may cause the signal discontinuity in the acceleration responses close to the damage location at the damage time instant. To this end, the damage detection on sudden stiffness reduction of building structures has been actively investigated in this study. The signal discontinuity of the structural acceleration responses of an example building is extracted based on the discrete wavelet transform. It is proved that the variation of the first level detail coefficients of the wavelet transform at damage instant is linearly proportional to the magnitude of the stiffness reduction. A new damage index is proposed and implemented to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. Numerical simulation using a five-story shear building under different types of excitation is carried out to assess the effectiveness and reliability of the proposed damage index for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also investigated. The made observations demonstrate that the proposed damage index can accurately identify the sudden damage events if the noise intensity is limited. PMID:24991647
Damage Detection on Sudden Stiffness Reduction Based on Discrete Wavelet Transform
Chen, Bo; Chen, Zhi-wei; Wang, Gan-jun; Xie, Wei-ping
2014-01-01
The sudden stiffness reduction in a structure may cause the signal discontinuity in the acceleration responses close to the damage location at the damage time instant. To this end, the damage detection on sudden stiffness reduction of building structures has been actively investigated in this study. The signal discontinuity of the structural acceleration responses of an example building is extracted based on the discrete wavelet transform. It is proved that the variation of the first level detail coefficients of the wavelet transform at damage instant is linearly proportional to the magnitude of the stiffness reduction. A new damage index is proposed and implemented to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. Numerical simulation using a five-story shear building under different types of excitation is carried out to assess the effectiveness and reliability of the proposed damage index for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also investigated. The made observations demonstrate that the proposed damage index can accurately identify the sudden damage events if the noise intensity is limited. PMID:24991647
Age, arterial stiffness, and components of blood pressure in Chinese adults.
Zheng, Meili; Xu, Xiping; Wang, Xiaobin; Huo, Yong; Xu, Xin; Qin, Xianhui; Tang, Genfu; Xing, Houxun; Fan, Fangfang; Cui, Wei; Yang, Xinchun
2014-12-01
Blood pressure (BP) changes with age. We conducted a cross-sectional study in rural Chinese adults to investigate: (1) what is the relationship between age, arterial stiffness, and BP in Chinese men and women; and (2) to what degree can the age-BP relationship be explained by arterial stiffness, controlling for other covariables. These analyses included a total of 1688 subjects (males/females: 623/1065), aged 40 to 88 years. Among them, 353 (20.9%) had hypertension (defined as systolic blood pressure (SBP) ≥ 140 mm Hg or diastolic blood pressure (DBP) ≥ 90 mm Hg). Arterial stiffness was measured by brachial-ankle pulse wave velocity (baPWV). baPWV appeared to be more strongly correlated with BP (including SBP, DBP, mean arterial pressure [MAP], pulse pressure [PP]) than age (P < 0.001 for comparisons between Spearman correlation coefficients). Furthermore, baPWV was associated with BP (including SBP, DBP, MAP, and PP) and risk of hypertension in a dose-response fashion, independent of age; in contrast, the age-BP associations were either attenuated or became negative after adjusting for baPWV. Arterial stiffness appears to be an independent contributor to hypertension, even after adjusting for age and other covariables. In contrast, age-BP associations became attenuated or negative after adjusting for baPWV. The utility of baPWV as a diagnostic, prognostic, and therapeutic indicator for hypertension warrants further investigation. PMID:25546666
NASA Technical Reports Server (NTRS)
Padovan, J.; Lackney, J.
1986-01-01
The current paper develops a constrained hierarchical least square nonlinear equation solver. The procedure can handle the response behavior of systems which possess indefinite tangent stiffness characteristics. Due to the generality of the scheme, this can be achieved at various hierarchical application levels. For instance, in the case of finite element simulations, various combinations of either degree of freedom, nodal, elemental, substructural, and global level iterations are possible. Overall, this enables a solution methodology which is highly stable and storage efficient. To demonstrate the capability of the constrained hierarchical least square methodology, benchmarking examples are presented which treat structure exhibiting highly nonlinear pre- and postbuckling behavior wherein several indefinite stiffness transitions occur.
NASA Technical Reports Server (NTRS)
Rosenbaum, J. S.
1971-01-01
Systems of ordinary differential equations in which the magnitudes of the eigenvalues (or time constants) vary greatly are commonly called stiff. Such systems of equations arise in nuclear reactor kinetics, the flow of chemically reacting gas, dynamics, control theory, circuit analysis and other fields. The research reported develops an A-stable numerical integration technique for solving stiff systems of ordinary differential equations. The method, which is called the generalized trapezoidal rule, is a modification of the trapezoidal rule. However, the method is computationally more efficient than the trapezoidal rule when the solution of the almost-discontinuous segments is being calculated.
Bending stiffness of conical and standard external fixator pins.
Oni, O O; Capper, M; Soutis, C
1993-10-01
The bending stiffnesses of a conical and a standard external fixator pin have been compared. The pins were inserted into pilot holes in a piece of teak hardwood and loads of different magnitudes were applied at a fixed moment arm. Force-deflection curves were obtained for each pin, and stiffness (newtons per metre) and percentage stiffness reduction were calculated for each pilot hole size. The results show that deflection increased (i.e. stiffness decreased) with increasing force or diameter of pilot hole. This loss of stiffness was linear for the standard pin but was bimodal for the conical pin. PMID:8286671
Commentary on Coefficient Alpha: A Cautionary Tale
ERIC Educational Resources Information Center
Green, Samuel B.; Yang, Yanyun
2009-01-01
The general use of coefficient alpha to assess reliability should be discouraged on a number of grounds. The assumptions underlying coefficient alpha are unlikely to hold in practice, and violation of these assumptions can result in nontrivial negative or positive bias. Structural equation modeling was discussed as an informative process both to
Decay of (p,q)-Fourier coefficients
Edmunds, David E.; Gurka, Petr; Lang, Jan
2014-01-01
We show that essentially the speed of decay of the Fourier sine coefficients of a function in a Lebesgue space is comparable to that of the corresponding coefficients with respect to the basis formed by the generalized sine functions sinp,q. PMID:25294961
Extreme damping in composite materials with negative-stiffness inclusions
NASA Astrophysics Data System (ADS)
Lakes, R. S.; Lee, T.; Bersie, A.; Wang, Y. C.
2001-03-01
When a force deforms an elastic object, practical experience suggests that the resulting displacement will be in the same direction as the force. This property is known as positive stiffness. Less familiar is the concept of negative stiffness, where the deforming force and the resulting displacement are in opposite directions. (Negative stiffness is distinct from negative Poisson's ratio, which refers to the occurrence of lateral expansion upon stretching an object.) Negative stiffness can occur, for example, when the deforming object has stored (or is supplied with) energy. This property is usually unstable, but it has been shown theoretically that inclusions of negative stiffness can be stabilized within a positive-stiffness matrix. Here we describe the experimental realization of this composite approach by embedding negative-stiffness inclusions of ferroelastic vanadium dioxide in a pure tin matrix. The resulting composites exhibit extreme mechanical damping and large anomalies in stiffness, as a consequence of the high local strains that result from the inclusions deforming more than the composite as a whole. Moreover, for certain temperature ranges, the negative-stiffness inclusions are more effective than diamond inclusions for increasing the overall composite stiffness. We expect that such composites could be useful as high damping materials, as stiff structural elements or for actuator-type applications.
Regional brain stiffness changes across the Alzheimer's disease spectrum☆
Murphy, Matthew C.; Jones, David T.; Jack, Clifford R.; Glaser, Kevin J.; Senjem, Matthew L.; Manduca, Armando; Felmlee, Joel P.; Carter, Rickey E.; Ehman, Richard L.; Huston, John
2015-01-01
Magnetic resonance elastography (MRE) is an MRI-based technique to noninvasively measure tissue stiffness. Currently well established for clinical use in the liver, MRE is increasingly being investigated to measure brain stiffness as a novel biomarker of a variety of neurological diseases. The purpose of this work was to apply a recently developed MRE pipeline to measure regional brain stiffness changes in human subjects across the Alzheimer's disease (AD) spectrum, and to gain insights into the biological processes underlying those stiffness changes by correlating stiffness with existing biomarkers of AD. The results indicate that stiffness changes occur mostly in the frontal, parietal and temporal lobes, in accordance with the known topography of AD pathology. Furthermore, stiffness in those areas correlates with existing imaging biomarkers of AD including hippocampal volumes and amyloid PET. Additional analysis revealed preliminary but significant evidence that the relationship between brain stiffness and AD severity is nonlinear and non-monotonic. Given that similar relationships have been observed in functional MRI experiments, we used task-free fMRI data to test the hypothesis that brain stiffness was sensitive to structural changes associated with altered functional connectivity. The analysis revealed that brain stiffness is significantly and positively correlated with default mode network connectivity. Therefore, brain stiffness as measured by MRE has potential to provide new and essential insights into the temporal dynamics of AD, as well as the relationship between functional and structural plasticity as it relates to AD pathophysiology. PMID:26900568
NASA Astrophysics Data System (ADS)
Shaw, A. D.; Neild, S. A.; Friswell, M. I.
2015-03-01
High Static Low Dynamic Stiffness (HSLDS) mounts consist of nonlinear springs that support a high static load with low static displacement, whilst maintaining locally low stiffness near equilibrium, to give a low natural frequency and consequently good isolation properties. Recent analysis has investigated such devices when the force-displacement relationship is an odd function about the equilibrium position, and analysed the consequences of different shapes of these functions. However many devices that have the HSLDS characteristic do not meet the assumptions of this analysis, in that the force-displacement relationship is generally asymmetric about equilibrium. Furthermore, even devices that do meet this assumption may be subject to significant adjustment error, particularly in the context of air vehicles where manoeuvres such as banked turns can cause an apparent variation in gravitational acceleration, and a consequent variation in the weight of the payload. This change in static load moves the payload away from its intended region of low stiffness. The current paper provides analysis of these situations, and shows that the performance of a mount with a symmetric stiffness-displacement relationship is highly sensitive to errors in the static loading. It is then shown that a mount with an asymmetric stiffness-displacement function can offer significant performance advantages when there are adjustment errors in the loading of the mount.
Normal stiffness calibration of microfabricated tri-layer conducting polymer actuators
NASA Astrophysics Data System (ADS)
Alici, Gursel; Higgins, Michael J.
2009-06-01
This paper reports on the stiffness characterization of microfabricated tri-layer conducting polymer (PPy) actuators. The rectangular, polypyrrole microactuators, which could operate both in aqueous and non-aqueous media, were fabricated using an excimer laser ablation technique that provided high throughput production and did not require cleanroom facilities. The microactuators were fixed at one end with electrical contacts and the other was end free to act as an electroactive microcantilever beam. An atomic force microscope (AFM) was used to measure the microactuator deflection under a range of normal forces applied by the AFM cantilever. A modified reference spring constant calibration method was employed to determine the stiffness constants of the microactuators. The stiffness of the microactuators in the electroactive (electrically stimulated) and passive state (no stimulation) were evaluated separately and compared. In doing so, the study presents results leading to the stiffness characterization of the first air-operated polymer microactuators and implementation of a simple, reliable and effective method for directly measuring the spring constant of polymer microactuators. This method is an alternative to the use of mechanical modeling methods, which can be difficult to implement for multi-layer (composite) polymer actuators. Importantly, our results highlight several requirements for using the reference spring method to accurately determine stiffness values of any microcantilever generally fabricated from soft, deformable materials.
Abiodun, O A; Akinoso, R
2015-05-01
The use of trifoliate yam (Dioscorea dumetorum) flour for stiff dough 'amala' production is one of the ways to curb under-utilization of the tuber. The study evaluates the textural and sensory properties of trifoliate yam flour and stiff dough. Freshly harvested trifoliate yam tubers were peeled, washed, sliced and blanched (60?()C for 10min). The sliced yam were soaked in water for 12h, dried and milled into flour. Pasting viscosities, functional properties, brown index and sensory attributes of the flour and stiff dough were analyzed. Peak, holding strength and final viscosities ranged from 84.09 to 213.33 RVU, 81.25 to 157.00 RVU and 127.58 to 236.17 RVU respectively. White raw flour had higher viscosity than the yellow flours. The swelling index, water absorption capacity and bulk density ranged from 1.46 to 2.28, 2.11 to 2.92ml H2O/g and 0.71 to 0.88g/cm(3) respectively. Blanching method employed improved the swelling index and water absorption capacity of flour. The brown index values of flour and stiff dough ranged from 6.73 to 18.36 and 14.63-46.72 respectively. Sensory evaluation revealed significant differences in the colour, odour and general acceptability of the product when compared with the stiff dough from white yam. PMID:25892788
Zhang, Zhaoyan; Chhetri, Dinesh K.; Bergeron, Jennifer L.
2014-01-01
Objective Medialization laryngoplasty is commonly used to treat glottic insufficiency. In this study, we investigated the effects of implant stiffness (Young’s modulus), medialization depth, and implant medial surface shape on acoustic outcomes. Study Design Basic science study using ex vivo laryngeal phonation model. Methods In an ex vivo human larynx phonation model, bilateral medialization laryngoplasties were performed with implants of varying stiffness, medial surface shape (rectangular, divergent and convergent), and varying depths of medialization. The subglottal pressure, the flow rate, and the outside sound were measured as the implant parameters were varied. Results Medialization through the use of implants generally improved the harmonic-to-noise ratio (HNR) and the number of harmonics excited in the outside sound spectra. The degree of acoustic improvement depended on the implant insertion depth, stiffness, and to a lesser degree implant shape. Varying implant insertion depth led to large variations in phonation for stiff implants, but had much smaller effects for soft implants. Conclusions Implants with stiffness comparable to vocal folds provided more consistent improvement in acoustic outcomes across different implant conditions. Further investigations are required to better understand the underlying mechanisms. PMID:25499519
Hilmy, S.I.; White, R.N.; Gergely, P.
1982-06-01
This report addresses four major topics in the general area of cracking and shear effects in concrete containment structures: (a) extensional stiffness of orthogonally reinforced flat concrete specimens subjected to tension in one direction only, (b) shear strength and shear stiffness of these same specimens when subjected to combined uniaxial tension and shear, (c) development of a preliminary analytical model for the prediction of the initial shear modulus and its degradation with increasing uniaxial tension levels, and (d) a comparative correlation of experimental results with results from earlier studies on similar specimens and on other types of shear specimens tested in many different laboratories. Eleven specimens with two-way orthogonal reinforcement were tested. Test parameters included the applied tension level (0, 0.3f/sub y/, 0.6f/sub y/, and 0.9f/sub y/), type of shear loading (monotonic and reversed cyclic), and level of applied shear stress. Prior to application of shear loading, measurements of extensional stiffness were conducted at reinforcing tension levels up to 0.6f/sub y/, and empirical expressions for crack width and extensional stiffness were derived. Stiffness degradation produced by subsequent shear loadings was also assessed.
Cell stiffness is a biomarker of the metastatic potential of ovarian cancer cells
NASA Astrophysics Data System (ADS)
Xu, Wenwei; Mezencev, Roman; Kim, Byungkyu; Wang, Lijuan; McDonald, John; Sulchek, Todd; Sulchek Team; McDonald Team
2013-03-01
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.
Initial damage influence of stiffness reduction for bronze route Nb 3 Sn strands
NASA Astrophysics Data System (ADS)
Luo, Wei; Zheng, X. J.
2011-10-01
Nb 3Sn strands are widely used in ITER CICCs, and the axial stiffness reduction induced by the initial damage in the form of filament breakage during processing of the composite strand is intensively related to the operation performance criteria. In this paper, an analytical model is developed to simulate this degradation of bronze route strands. The model contains three sub-models: the effective modulus of a filament with initial damage is investigated by a shear-lag model based on the global load sharing scheme and Weibull fiber strength statistics; the weakened stiffness of the superconducting layer is deduced by the Mori-Tanaka model; and the effective axial modulus of the strand is obtained by the multilayered generalized self-consistent model. The results indicate that the stiffness reduction of a strand presents obvious nonlinear behavior and depends on the initial damage parameter and the evolution of total damage.
Nanocharacterization of the negative stiffness of ferroelectric materials
NASA Astrophysics Data System (ADS)
Alipour Skandani, A.; Ctvrtlik, R.; Al-Haik, M.
2014-08-01
Phase changing materials such as ferroelectric materials could exhibit negative stiffness under certain thermomechanical environments. This negative stiffness is embodied by a deflection along the opposite direction of the applied load. So far negative stiffness materials were investigated with the specific morphology of embedded inclusions in stiff matrices then the resulting composite is studied to measure the behavior of each constituent indirectly. In this study, a modified nonisothermal nanoindentation method is developed to measure the negative stiffness of triglycine sulfate single crystal directly. This in-situ method is intended to first demonstrate the feasibility of detecting the negative stiffness via nanoindentation and nanocreep of a ferroelectric material at its Curie point and then to quantify the negative stiffness without the need for embedding the crystal within a stiffer matrix.
Laser application on haptics: Tactile stiffness measurement
NASA Astrophysics Data System (ADS)
Scalise, L.; Memeo, M.; Cannella, F.; Valente, M.; Caldwell, D. G.; Tomasini, E. P.
2012-06-01
There is a great interest in exploring the proprieties of the sense of the touch, its detailed knowledge in fact is a key issue in the area of robotics, haptics and human-machine interaction. In this paper, the authors focus their attention on a novel measurement method for the assessment of the tactile stiffness based on a original test rig; tactile stiffness is defined as the ratio between force, exerted by the finger, and the displacement of the finger tip operated during the test. To reach this scope, the paper describes a specific experimental test-rig used for the evaluation of subject tactile sensitivity, where finger force applied during tests as well as displacement and velocity of displacement, operated by the subject under investigation, are measured. Results show that tactile stiffness is linear respect to stimuli spatial difference (which is proportional to the difficulty to detect the variation of them). In particular, it has been possible to relate the force and displacement measured during the tests. The relationship between the response of the subject to the grating, velocity and force is determined. These results permit to carry out the further experimental tests on the same subject avoiding the use of a load cell and therefore simplifying the measurement test rig and data post-processing. Indeed, the first aspect (use of a load cell) can be relevant, because the grating positions are different, requiring a specific re-calibration and setting before each trial; while the second aspect allows simplify the test rig complexity and the processing algorithm.
An improved spinning lens test to determine the stiffness of the human lens
Burd, H.J.; Wilde, G.S.; Judge, S.J.
2011-01-01
It is widely accepted that age-related changes in lens stiffness are significant for the development of presbyopia. However, precise details on the relative importance of age-related changes in the stiffness of the lens, in comparison with other potential mechanisms for the development of presbyopia, have not yet been established. One contributing factor to this uncertainty is the paucity and variability of experimental data on lens stiffness. The available published data generally indicate that stiffness varies spatially within the lens and that stiffness parameters tend to increase with age. However, considerable differences exist between these published data sets, both qualitatively and quantitatively. The current paper describes new and improved methods, based on the spinning lens approach pioneered by Fisher, R.F. (1971) The elastic constants of the human lens, Journal of Physiology, 212, 147180, to make measurements on the stiffness of the human lens. These new procedures have been developed in an attempt to eliminate, or at least substantially reduce, various systematic errors in Fishers original experiment. An improved test rig has been constructed and a new modelling procedure for determining lens stiffness parameters from observations made during the test has been devised. The experiment involves mounting a human lens on a vertical rotor so that the lens spins on its optical axis (typically at 1000rpm). An automatic imaging system is used to capture the outline of the lens, while it is rotating, at pre-determined angular orientations. These images are used to quantify the deformations developed in the lens as a consequence of the centripetal forces induced by the rotation. Lens stiffness is inferred using axisymmetric finite element inverse analysis in which a nearly-incompressible neo-Hookean constitutive model is used to represent the mechanics of the lens. A numerical optimisation procedure is used to determine the stiffness parameters that provide a best fit between the finite element model and the experimental data. Sample results are presented for a human lens of age 33 years. PMID:21040722
On waveguide modeling of stiff piano strings
NASA Astrophysics Data System (ADS)
Ducasse, ric
2005-09-01
Bensa et al. [J. Acoust. Soc. Am. 114, 1095-1107 (2003), Sec. IV] recently proposed a waveguide model for the transverse displacement of a stiff piano string. The study described here is an attempt to cast a complementary light on this topic, based on a common wave approach instead of a modal approach. A pair of weakly attenuated traveling waves and a pair of fast-decaying waves both satisfy the one-dimensional wave equation developed by Bensa et al. These solutions have to be carefully considered, however, for portions of string interacting with the hammer felt, the bridge, or the capo d'astro bar.
Spin stiffness of vector spin glasses
NASA Astrophysics Data System (ADS)
Beyer, Frank; Weigel, Martin
2011-09-01
We study domain-wall excitations for O(m) vector spin glasses in the limit m→∞, where the energy landscape is simplified considerably compared to XY or Heisenberg models due to the complete disappearance of metastability. Using numerical ground-state calculations and appropriate pairs of complementary boundary conditions, domain-wall defects are inserted into the systems and their excitation energies are measured. This allows us to determine the stiffness exponents for lattices of a range of spatial dimensions d=2,…,7. Compiling these results, we can finally determine the lower critical dimension of the model. The outcome is compared to estimates resulting from field-theoretic calculations.
POST-TRAUMATIC STIFFNESS OF THE ELBOW
Filh, Geraldo Motta; Galvão, Marcus Vinicius
2015-01-01
Elbow stiffness is a common problem after joint trauma, causing functional impairment of the upper limb. The severity of the dysfunction depends on the nature of the initial trauma and the treatment used. Appropriate clinical evaluation and complementary examinations are essential for therapeutic planning. Several surgical techniques are now available and the recommendation must be made in accordance with patient characteristics, degree of joint limitation and the surgeon's skill. Joint incongruence and degeneration have negative effects on the prognosis, but heterotrophic ossification alone has been correlated with a favorable surgical prognosis.
An Ordinal Coefficient of Relational Agreement for Multiple Judges.
ERIC Educational Resources Information Center
Fagot, Robert F.
1994-01-01
A previous paper proposed a generalized family of coefficients of relational agreement for multiple judges. It focused on the concept of empirically meaningful relationships. This paper presents an ordinal coefficient of relational agreement as a special case of the generalized family. The proposed ordinal coefficient encompasses other ordinal
NASA Technical Reports Server (NTRS)
Lim, T. C.; Singh, R.
1990-01-01
How vibratory motion can be transmitted from the rotating shaft to the casing and other connecting structures in rotating mechanical equipment is addressed here by developing a new mathematical model of precision rolling element bearings. A new grating stiffness matrix is proposed in order to demonstrate a coupling between the shaft bending motion and the flexural motion of the casing plate. It is shown that the translational bearing stiffness coefficients currently used in rotor dynamic models are a small subset of the proposed matrix. The theory is validated by examples, and the proposed bearing formulation is then extended to demonstrate its superiority over existing models in vibration transmission analyses. It is shown that the model can easily be incorporated into analytical or numerical models typically used for dynamic analyses.
Investigating bias in squared regression structure coefficients
Nimon, Kim F.; Zientek, Linda R.; Thompson, Bruce
2015-01-01
The importance of structure coefficients and analogs of regression weights for analysis within the general linear model (GLM) has been well-documented. The purpose of this study was to investigate bias in squared structure coefficients in the context of multiple regression and to determine if a formula that had been shown to correct for bias in squared Pearson correlation coefficients and coefficients of determination could be used to correct for bias in squared regression structure coefficients. Using data from a Monte Carlo simulation, this study found that squared regression structure coefficients corrected with Pratt's formula produced less biased estimates and might be more accurate and stable estimates of population squared regression structure coefficients than estimates with no such corrections. While our findings are in line with prior literature that identified multicollinearity as a predictor of bias in squared regression structure coefficients but not coefficients of determination, the findings from this study are unique in that the level of predictive power, number of predictors, and sample size were also observed to contribute bias in squared regression structure coefficients. PMID:26217273
Identifying Bearing Rotordynamic Coefficients using an Extended Kalman Filter
NASA Technical Reports Server (NTRS)
Miller, Brad A.; Howard, Samuel A.
2008-01-01
An Extended Kalman Filter is developed to estimate the linearized direct and indirect stiffness and damping force coefficients for bearings in rotor-dynamic applications from noisy measurements of the shaft displacement in response to imbalance and impact excitation. The bearing properties are modeled as stochastic random variables using a Gauss-Markov model. Noise terms are introduced into the system model to account for all of the estimation error, including modeling errors and uncertainties and the propagation of measurement errors into the parameter estimates. The system model contains two user-defined parameters that can be tuned to improve the filter s performance; these parameters correspond to the covariance of the system and measurement noise variables. The filter is also strongly influenced by the initial values of the states and the error covariance matrix. The filter is demonstrated using numerically simulated data for a rotor-bearing system with two identical bearings, which reduces the number of unknown linear dynamic coefficients to eight. The filter estimates for the direct damping coefficients and all four stiffness coefficients correlated well with actual values, whereas the estimates for the cross-coupled damping coefficients were the least accurate.
Identifying Bearing Rotodynamic Coefficients Using an Extended Kalman Filter
NASA Technical Reports Server (NTRS)
Miller, Brad A.; Howard, Samuel A.
2008-01-01
An Extended Kalman Filter is developed to estimate the linearized direct and indirect stiffness and damping force coefficients for bearings in rotor dynamic applications from noisy measurements of the shaft displacement in response to imbalance and impact excitation. The bearing properties are modeled as stochastic random variables using a Gauss-Markov model. Noise terms are introduced into the system model to account for all of the estimation error, including modeling errors and uncertainties and the propagation of measurement errors into the parameter estimates. The system model contains two user-defined parameters that can be tuned to improve the filter's performance; these parameters correspond to the covariance of the system and measurement noise variables. The filter is also strongly influenced by the initial values of the states and the error covariance matrix. The filter is demonstrated using numerically simulated data for a rotor bearing system with two identical bearings, which reduces the number of unknown linear dynamic coefficients to eight. The filter estimates for the direct damping coefficients and all four stiffness coefficients correlated well with actual values, whereas the estimates for the cross-coupled damping coefficients were the least accurate.
Coefficients of Effective Length.
ERIC Educational Resources Information Center
Edwards, Roger H.
1981-01-01
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)
2013-01-01
Background Independent of other cardiovascular (CV) risk factors, increased arterial stiffness has been established as a predictor of morbidity and mortality. The main aim of this study was to investigate the impact of diabetes on arterial stiffness in a representative sample of an urban Brazilian population plus Amerindians. Methods A total of 1,415 individuals from the general population were randomly selected plus 588 Amerindians from a native community in Brazil. In addition, a sub-sample of 380 individuals from the general population had 5-year follow-up data. Pulse wave velocity (PWV) was measured with a non-invasive automatic device (Complior, Colson; Garges les Gonesses, France) and increased arterial stiffness was defined as PWV???12 m/s. Results In the overall group, diabetic individuals had higher frequencies of increased arterial stiffness and hypertension. They also had higher values of PWV, body mass index, total cholesterol, triglycerides, systolic and diastolic blood pressures compared to non-diabetic individuals (p?stiffness frequency were higher in diabetic individuals in both groups (hypertensive and non-hypertensive) (p?stiffness was observed in the diabetic individuals from the overall group (OR?=?2.27; CI?=?1.47-3.52, p?stiffness compared to non-diabetic individuals. Both diabetic and non-diabetic individuals had higher PWV values after 5 years. There was no significant difference in the 5-year PWV progression in diabetic compared to non-diabetic individuals. Conclusions These results confirm, in a sample of Brazilian population, that the presence of diabetes is associated with increased arterial stiffness and it may contribute in part to increased cardiovascular risk in diabetic patients. PMID:23965633
Transport coefficients of quantum plasmas
Bennaceur, D.; Khalfaoui, A.H. )
1993-09-01
Transport coefficients of fully ionized plasmas with a weakly coupled, completely degenerate electron gas and classical ions with a wide range of coupling strength are expressed within the Bloch transport equation. Using the Kohler variational principle the collision integral of the quantum Boltzmann equation is derived, which accounts for quantum effects through collective plasma oscillations. The physical implications of the results are investigated through comparisons with other theories. For practical applications, electrical and thermal conductivities are derived in simple analytical formulas. The relation between these two transport coefficients is expressed in an explicit form, giving a generalized Wiedemann-Franz law, where the Lorentz ratio is a dependent function of the coupling parameter and the degree of degeneracy of the plasma.
Edman, K A; Lou, F
1990-01-01
1. Changes in force and stiffness were recorded simultaneously during 1 s isometric (fixed ends) tetani of single fibres isolated from the anterior tibialis muscle of Rana temporaria (temperature 1-3 degrees C; sarcomere length, 2.10 micron). Stiffness was measured as the change in force that occurred in response to a 4 kHz sinusoidal length oscillation of the fibre. Some experiments were performed in which stiffness was determined from a fast (0.2 ms) length step that was applied to a 'tendon-free' segment of the muscle fibre during the tetanus plateau. 2. A moderate degree of fatigue was produced by decreasing the time between tetani from 300 s (control) to 15 s. By this treatment the maximum tetanic force (Ftet) was reversibly reduced to 70-75% of the control value. Maximum tetanic stiffness (Stet) was related to Ftet according to the following regression (both variables expressed as percentage of their control values): Stet = 0.369 Ftet + 62.91 (correlation coefficient, 0.95; P less than 0.001). A 25% decrease in isometric force during fatigue was thus associated with merely 9% reduction of fibre stiffness. 3. Whereas the rate of rise of force during tetanus was markedly reduced by fatiguing stimulation, the rate of rise of stiffness was only slightly affected. 4. Intracellular acidification (produced by raised extracellular CO2 concentration) largely reproduced the contractile changes observed during fatigue. However, for a given decrease in tetanic force there was a smaller reduction in fibre stiffness during acidosis than during fatigue. 5. Caffeine (0.5 mM) added to the fibre after development of fatigue and intracellular acidosis greatly potentiated the isometric twitch but did not affect maximum tetanic force. This finding provides evidence that the contractile system was fully activated during the tetanus plateau both in the fatigued state and during acidosis. 6. The results suggest that the decrease in contractile strength after frequent tetanization (intervals between tetani, 15 s) is attributable to altered kinetics of cross-bridge function leading to reduced number of active cross-bridges and, most significantly, to reduced force output of the individual bridge. The possible role of increased intracellular H+ concentration in the development of muscle fatigue is discussed. PMID:2391650
Stiffness Dependent Separation of Cells in a Microfluidic Device
NASA Astrophysics Data System (ADS)
Sulchek, Todd; Wang, Gonghao; Mao, Wenbin; Henegar, Caitlin; Alexeev, Alexander
2012-02-01
Abnormal cell mechanical stiffness can point to the development of various diseases including cancers and infections. We report a new high-throughput technique for continuous cell separation utilizing variation in cell stiffness. We use a microfluidic channel decorated by periodic diagonal ridges to separate K562 lymphoblastic cell line modified to different mechanical stiffness values. Diagonal ridges within the microfluidic flow channel compress and deform the cells in rapid succession to translate each cell perpendicular to the channel axis in proportion to its stiffness. Atomic force microscopy (AFM) was used to directly measure the Young's modulus of modified K562 cells to verify the stiffness variation. We demonstrate that soft cells can be separated from stiff cells at physiological concentrations with a fivefold enrichment of cell populations. This microfluidic device opens the way for conducting rapid and low-cost cell analysis and purification through physical markers.
Postprandial effects on arterial stiffness parameters in healthy young adults.
Murray, Tyler; Yang, Eric Y; Brunner, Gerd; Kumar, Anirudh; Lakkis, Nasser; Misra, Arunima; Virani, Salim S; Hartley, Craig J; Morrisett, Joel D; Ballantyne, Christie M; Nambi, Vijay
2015-12-01
Postprandial lipemia has been associated with acute endothelial dysfunction. Endothelial dysfunction, in turn, is associated with increased arterial stiffness. However, the relationship between postprandial lipemia and acute changes in arterial stiffness has not been extensively investigated. Therefore, we conducted a pilot study on the effects of postprandial lipemia on arterial stiffness in 19 healthy young adults before and after consumption of a high-fat mixed meal. Arterial stiffness was assessed locally with echo-tracking carotid arterial strain (CAS) and globally with carotid-femoral pulse wave velocity (PWV). As assessed by these two benchmark parameters, arterial stiffness did not differ significantly postprandially. However, the arterial distension period (ADP) was significantly lower 2 hours after mixed meal ingestion. In addition, slopes of carotid artery area (CAA) curves were significantly steeper postprandially. Therefore, we concluded that ADP may be a more sensitive marker of arterial stiffness in healthy young adults when compared to PWV and CAS. PMID:26060082
A nonlinear negative stiffness metamaterial unit cell and small-on-large multiscale material model
NASA Astrophysics Data System (ADS)
Klatt, Timothy; Haberman, Michael R.
2013-07-01
A persistent challenge in the design of composite materials is the ability to fabricate materials that simultaneously display high stiffness and high loss factors for the creation of structural elements capable of passively suppressing vibro-acoustic energy. Relevant recent research has shown that it is possible to produce composite materials whose macroscopic mechanical stiffness and loss properties surpass those of conventional composites through the addition of trace amounts of materials displaying negative stiffness (NS) induced by phase transformation [R. S. Lakes et al., Nature 410, 565-567 (2001)]. The present work investigates the ability to elicit NS behavior without employing physical phenomena such as inherent nonlinear material behavior (e.g., phase change or plastic deformation) or dynamic effects, but rather the controlled buckling of small-scale structural elements, metamaterials, embedded in a continuous viscoelastic matrix. To illustrate the effect of these buckled elements, a nonlinear hierarchical multiscale material model is derived, which estimates the macroscopic stiffness and loss of a composite material containing pre-strained microscale structured inclusions. The multiscale model consists of two scale transition models, the first being an energy-based nonlinear finite element (FE) method to determine the tangent modulus of the metamaterial unit cell, and the other a classical analytical micromechanical model to determine the effective stiffness and loss tensors of a heterogeneous material for small perturbations from the local strain state of the unit cells. The FE method enables the estimation of an effective nonlinear anisotropic stiffness tensor of a buckled microstructure that produces NS and is sufficiently general to consider geometries different from those given in this work.
Experiments on dynamic stiffness and damping of tapered bore seals
NASA Technical Reports Server (NTRS)
Fleming, David P.
1987-01-01
Stiffness and damping were measured in tapered bore ring seals with air as the sealed fluid. Excitation was provided by a known unbalance in the shaft which rotated in the test seals. Results were obtained for various seal supply pressures, clearances, unbalance amounts, and shaft speeds. Stiffness and damping varied little with unbalance level, indicating linearity of the seal. Greater variation was observed with speed and particularly supply pressure. A one-dimensional analysis predicted stiffness fairly well, but considerably overestimated damping.
Melo, Xavier; Fernhall, Bo; Santos, Diana A; Pinto, Rita; Pimenta, Nuno M; Sardinha, Luís B; Santa-Clara, Helena
2016-03-01
This study compared the effects of a bout of maximal running exercise on arterial stiffness in children and adults. Right carotid blood pressure and artery stiffness indices measured by pulse wave velocity (PWV), compliance and distensibility coefficients, stiffness index α and β (echo-tracking), contralateral carotid blood pressure, and upper and lower limb and central/aortic PWV (applanation tonometry) were taken at rest and 10 min after a bout of maximal treadmill running in 34 children (7.38 ± 0.38 years) and 45 young adults (25.22 ± 0.91 years) having similar aerobic potential. Two-by-two repeated measures analysis of variance and analysis of covariance were used to detect differences with exercise between groups. Carotid pulse pressure (PP; η(2) = 0.394) increased more in adults after exercise (p < 0.05). Compliance (η(2) = 0.385) decreased in particular in adults and in those with high changes in distending pressure, similarly to stiffness index α and β. Carotid PWV increased more in adults and was related to local changes in PP but not mean arterial pressure (MAP). Stiffness in the lower limbs decreased (η(2) = 0.115) but apparently only in those with small MAP changes (η(2) = 0.111). No significant exercise or group interaction effects were found when variables were adjusted to height. An acute bout of maximal exercise can alter arterial stiffness and hemodynamics in the carotid artery and within the active muscle beds. Arterial stiffness and hemodynamic response to metabolic demands during exercise in children simply reflect their smaller body size and may not indicate a particular physiological difference compared with adults. PMID:26842667
Ellison, Michelle; Kobayashi, Hirohito; Delaney, Fern; Danielson, Kelson; Vanderby, Ray; Muir, Peter; Forrest, Lisa J
2014-01-01
B-mode ultrasound is an established imaging modality for evaluating canine tendon injury. However, full extent of tendon injury often remains difficult to estimate, as small changes in sonographic appearance are associated with large changes in biomechanical strength. The acoustoelastic strain gauge (ASG) is an ultrasound-based tissue evaluation technique that relates the change in echo intensity observed during relaxation or stretching of tendons to the tissue’s mechanical properties. This technique deduces stiffness gradient (the rate of change of normalized stiffness as a function of tissue strain) by analyzing the ultrasound dynamic images captured from gradually deforming tissue. Acoustoelastic strain gauge has been proven to accurately model strain and stiffness within tendons in vitro. To determine the feasibility and repeatability for in vivo ASG measurements of canine tendon function, stiffness gradients for the gastrocnemius tendons of ten clinically normal dogs were recorded by two non-independent observers at three sites (musculotendinous junction, mid tendon, and insertion). Average stiffness gradient indices (0.0132, 0.0141, 0.0136) and dispersion values (0.0053, 0.0054, 0.0057) for each site, respectively, were consistent with published mechanical properties for normal canine tendon. Mean differences of the average stiffness gradient index and dispersion value between observers and between limbs for each site were less than 16%. Using interclass coefficients (ICC), intraobserver (ICC 0.79–0.98) and interobserver (ICC 0.77–0.95) reproducibility was good to excellent. Right and left limb values were symmetric (ICC 0.74–0.92). Findings from this study indicated that ASG is a feasible and repeatable technique for measuring stiffness gradients in canine tendons. PMID:23663072
Lucas, Kelsey N; Thornycroft, Patrick J M; Gemmell, Brad J; Colin, Sean P; Costello, John H; Lauder, George V
2015-10-01
Simple mechanical models emulating fish have been used recently to enable targeted study of individual factors contributing to swimming locomotion without the confounding complexity of the whole fish body. Yet, unlike these uniform models, the fish body is notable for its non-uniform material properties. In particular, flexural stiffness decreases along the fish's anterior-posterior axis. To identify the role of non-uniform bending stiffness during fish-like propulsion, we studied four foil model configurations made by adhering layers of plastic sheets to produce discrete regions of high (5.5נ10(-5) Nm(2)) and low (1.9נ10(-5) Nm(2)) flexural stiffness of biologically-relevant magnitudes. This resulted in two uniform control foils and two foils with anterior regions of high stiffness and posterior regions of low stiffness. With a mechanical flapping foil controller, we measured forces and torques in three directions and quantified swimming performance under both heaving (no pitch) and constant 0 angle of attack programs. Foils self-propelled at Reynolds number 21 000-115 000 and Strouhal number ?0.20-0.25, values characteristic of fish locomotion. Although previous models have emphasized uniform distributions and heaving motions, the combination of non-uniform stiffness distributions and 0 angle of attack pitching program was better able to reproduce the kinematics of freely-swimming fish. This combination was likewise crucial in maximizing swimming performance and resulted in high self-propelled speeds at low costs of transport and large thrust coefficients at relatively high efficiency. Because these metrics were not all maximized together, selection of the 'best' stiffness distribution will depend on actuation constraints and performance goals. These improved models enable more detailed, accurate analyses of fish-like swimming. PMID:26447541
Recent Advances in Hypertension: Arterial Stiffness and Hypertension
Mitchell, Gary F.
2014-01-01
Over the past decade, increased aortic stiffness has emerged as an important risk factor for target organ damage and cardiovascular disease events. Aortic stiffness can be assessed as pulse wave velocity (PWV), which is a measure of aortic wall stiffness, and pulse pressure (PP), which is affected by wall stiffness and the interaction between flow and diameter. Because these stiffness measures have different sensitivities to geometry and other factors, they are only moderately correlated and play a complementary role in risk prediction. Arterial stiffness has long been viewed as a complication of hypertension that integrates long-term adverse effects of elevated blood pressure and other risk factors. However, PWV is only modestly correlated with risk factors other than age and blood pressure, which likely explains the ability of PWV to add to standard risk prediction models and reclassify risk in a clinically relevant manner. Recent studies have demonstrated that stiffness can antedate and contribute to the pathogenesis of hypertension, raising the possibility that early assessment of arterial stiffness may provide insight into complications including hypertension that develop years later. The role that stiffness plays in the pathogenesis of hypertension and cardiovascular disease has sparked considerable interest in defining basic mechanisms that stiffen the aortic wall, increase PP and contribute to target organ damage with a hope that elucidation of these mechanisms will allow for development of more effective treatments. PMID:24752432
Synthesis of stiffness and mass matrices from experimental vibration modes.
NASA Technical Reports Server (NTRS)
Ross, R. G., Jr.
1971-01-01
With highly complex structures, it is sometimes desirable to derive a dynamic model of the system from experimental vibration data. This paper presents algorithms for synthesizing the mass and stiffness matrices from experimentally derived modal data in a way which preserves the physical significance of the individual mass and stiffness elements. The synthesizing procedures allow for the incorporation of other mass and stiffness data, whether empirical or based on the analyst's insight. The mass and stiffness matrices are derived for a cantilever beam example and are compared with those obtained using earlier techniques.
Towards ultra-stiff materials: Surface effects on nanoporous materials
Lu, Dingjie; Xie, Yi Min; Huang, Xiaodong; Zhou, Shiwei; Li, Qing
2014-09-08
The significant rise in the strength and stiffness of porous materials at nanoscale cannot be described by conventional scaling laws. This letter investigates the effective Young's modulus of such materials by taking into account surface effect in a microcellular architecture designed for an ultralight material whose stiffness is an order of magnitude higher than most porous materials. We find that by considering the surface effects the predicted stiffness using Euler-Bernoulli beam theory compares well to experimental data for spongelike nanoporous gold with random microstructures. Analytical results show that, of the two factors influencing the effective Young's modulus, the residual stress is more important than the surface stiffness.
Prevention and treatment of elbow stiffness: a 5-year update.
Everding, Nathan G; Maschke, Steven D; Hoyen, Harry A; Evans, Peter J
2013-12-01
Elbow stiffness is a challenging and common problem faced by upper extremity surgeons. Although functional improvements can be made with both nonsurgical and surgical management strategies, physicians must remain vigilant with efforts to prevent stiffness before it starts. Recent advancements in the biology and pathology of elbow contracture have led to improved understanding of this difficult problem, and they may lead to future breakthroughs in the prevention and treatment of elbow stiffness. This article serves as an update to our previous review of elbow stiffness, focusing on recent advancements in the past 5 years, as well as updating our current algorithm for treatment. PMID:24210721
Östling, Gerd; Nilsson, Peter M.
2015-01-01
Introduction Arterial stiffness is an independent risk factor for cardiovascular morbidity and can be assessed by applanation tonometry by measuring pulse wave velocity (PWV) and augmentation index (AIX) by pressure pulse wave analysis (PWA). As an inexpensive and operator independent alternative, photoelectric plethysmography (PPG) has been introduced with analysis of the digital volume pulse wave (DPA) and its second derivatives of wave reflections. Objective The objective was to investigate the repeatability of arterial stiffness parameters measured by digital pulse wave analysis (DPA) and the associations to applanation tonometry parameters. Methods and Results 112 pregnant and non-pregnant individuals of different ages and genders were examined with SphygmoCor arterial wall tonometry and Meridian DPA finger photoplethysmography. Coefficients of repeatability, Bland-Altman plots, intraclass correlation coefficients and correlations to heart rate (HR) and body height were calculated for DPA variables, and the DPA variables were compared to tonometry variables left ventricular ejection time (LVET), PWV and AIX. No DPA variable showed any systematic measurement error or excellent repeatability, but dicrotic index (DI), dicrotic dilatation index (DDI), cardiac ejection elasticity index (EEI), aging index (AI) and second derivatives of the crude pulse wave curve, b/a and e/a, showed good repeatability. Overall, the correlations to AIX were better than to PWV, with correlations coefficients >0.70 for EEI, AI and b/a. Considering the level of repeatability and the correlations to tonometry, the overall best DPA parameters were EEI, AI and b/a. The two pansystolic time parameters, ejection time compensated (ETc) by DPA and LVET by tonometry, showed a significant but weak correlation. Conclusion For estimation of the LV function, ETc, EEI and b/a are suitable, for large artery stiffness EEI, and for small arteries DI and DDI. The only global parameter, AI, showed a high repeatability and the overall best correlations with AIX and PWV. PMID:26291079
Stiffness of ? subunit of F(1)-ATPase.
Okuno, Daichi; Iino, Ryota; Noji, Hiroyuki
2010-11-01
F(1)-ATPase is a molecular motor in which the ? subunit rotates inside the ?(3)?(3) ring upon adenosine triphosphate (ATP) hydrolysis. Recent works on single-molecule manipulation of F(1)-ATPase have shown that kinetic parameters such as the on-rate of ATP and the off-rate of adenosine diphosphate (ADP) strongly depend on the rotary angle of the ? subunit (Hirono-Hara et al. 2005; Iko et al. 2009). These findings provide important insight into how individual reaction steps release energy to power F(1) and also have implications regarding ATP synthesis and how reaction steps are reversed upon reverse rotation. An important issue regarding the angular dependence of kinetic parameters is that the angular position of a magnetic bead rotation probe could be larger than the actual position of the ? subunit due to the torsional elasticity of the system. In the present study, we assessed the stiffness of two different portions of F(1) from thermophilic Bacillus PS3: the internal part of the ? subunit embedded in the ?(3)?(3) ring, and the complex of the external part of the ? subunit and the ?(3)?(3) ring (and streptavidin and magnetic bead), by comparing rotational fluctuations before and after crosslinkage between the rotor and stator. The torsional stiffnesses of the internal and remaining parts were determined to be around 223 and 73 pNnm/radian, respectively. Based on these values, it was estimated that the actual angular position of the internal part of the ? subunit is one-fourth of the magnetic bead position upon stalling using an external magnetic field. The estimated elasticity also partially explains the accommodation of the intrinsic step size mismatch between F(o) and F(1)-ATPase. PMID:20549499
NASA Technical Reports Server (NTRS)
Snyder, G. Jeffrey (Inventor)
2015-01-01
A high temperature Seebeck coefficient measurement apparatus and method with various features to minimize typical sources of errors is described. Common sources of temperature and voltage measurement errors which may impact accurate measurement are identified and reduced. Applying the identified principles, a high temperature Seebeck measurement apparatus and method employing a uniaxial, four-point geometry is described to operate from room temperature up to 1300K. These techniques for non-destructive Seebeck coefficient measurements are simple to operate, and are suitable for bulk samples with a broad range of physical types and shapes.
JKTLD: Limb darkening coefficients
NASA Astrophysics Data System (ADS)
Southworth, John
2015-11-01
JKTLD outputs theoretically-calculated limb darkening (LD) strengths for equations (LD laws) which predict the amount of LD as a function of the part of the star being observed. The coefficients of these laws are obtained by bilinear interpolation (in effective temperature and surface gravity) in published tables of coefficients calculated from stellar model atmospheres by several researchers. Many observations of stars require the strength of limb darkening (LD) to be estimated, which can be done using theoretical models of stellar atmospheres; JKTLD can help in these circumstances.
Vichare, Shirish; Sen, Shamik; Inamdar, Mandar M
2014-02-28
Mechanosensing by adherent cells is usually studied by quantifying cell responses on hydrogels that are covalently linked to a rigid substrate. Atomic force microscopy (AFM) represents a convenient way of characterizing the mechanoadaptation response of adherent cells on hydrogels of varying stiffness and thickness. Since AFM measurements reflect the effective cell stiffness, therefore, in addition to measuring real cytoskeletal alterations across different conditions, these measurements might also be influenced by the geometry and physical properties of the substrate itself. To better understand how the physical attributes of the gel influence AFM stiffness measurements of cells, we have used finite element analysis to simulate the indentation of cells of various spreads resting on hydrogels of varying stiffness and thickness. Consistent with experimental results, our simulation results indicate that for well spread cells, stiffness values are significantly over-estimated when experiments are performed on cells cultured on soft and thin gels. Using parametric studies, we have developed scaling relationships between the effective stiffness probed by AFM and the bulk cell stiffness, taking cell and tip geometry, hydrogel properties, nuclear stiffness and cell contractility into account. Finally, using simulated mechanoadaptation responses, we have demonstrated that a cell stiffening response may arise purely due to the substrate properties. Collectively, our results demonstrate the need to take hydrogel properties into account while estimating cell stiffness using AFM indentation. PMID:24651595
The fully implicit stochastic-{alpha} method for stiff stochastic differential equations
Safique Ahmad, Sk. Chandra Parida, Nigam Raha, Soumyendu
2009-12-01
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.
ERIC Educational Resources Information Center
Mohammed, Ahmed; Zeleke, Aklilu
2015-01-01
We introduce a class of second-order ordinary differential equations (ODEs) with variable coefficients whose closed-form solutions can be obtained by the same method used to solve ODEs with constant coefficients. General solutions for the homogeneous case are discussed.
Three-dimensional stiffness of the carpal arch.
Gabra, Joseph N; Li, Zong-Ming
2016-01-01
The carpal arch of the wrist is formed by irregularly shaped carpal bones interconnected by numerous ligaments, resulting in complex structural mechanics. The purpose of this study was to determine the three-dimensional stiffness characteristics of the carpal arch using displacement perturbations. It was hypothesized that the carpal arch would exhibit an anisotropic stiffness behavior with principal directions that are oblique to the conventional anatomical axes. Eight (n=8) cadavers were used in this study. For each specimen, the hamate was fixed to a custom stationary apparatus. An instrumented robot arm applied three-dimensional displacement perturbations to the ridge of trapezium and corresponding reaction forces were collected. The displacement-force data were used to determine a three-dimensional stiffness matrix using least squares fitting. Eigendecomposition of the stiffness matrix was used to identify the magnitudes and directions of the principal stiffness components. The carpal arch structure exhibited anisotropic stiffness behaviors with a maximum principal stiffness of 16.4±4.6N/mm that was significantly larger than the other principal components of 3.1±0.9 and 2.6±0.5N/mm (p<0.001). The principal direction of the maximum stiffness was pronated within the cross section of the carpal tunnel which is accounted for by the stiff transverse ligaments that tightly bind distal carpal arch. The minimal principal stiffness is attributed to the less constraining articulation between the trapezium and scaphoid. This study provides advanced characterization of the wrist׳s three-dimensional structural stiffness for improved insight into wrist biomechanics, stability, and function. PMID:26617368
NASA Technical Reports Server (NTRS)
Fritsche, H.
1983-01-01
An attempt is made to judge the value of the Gaussian series for the Earth's magnetism. The computation employed to do this uses the method of the least and greatest coefficients. The number of unknown which had to be calculated from the individual groups was at most only four. All symbols of Gauss were retained.
Akgl, Turgut; Gksan, Sleyman Bora; Eren, ?lker
2014-01-01
INTRODUCTION There are various complications reported with surgical treatment of DDH. Most studied complication is avascular necrosis of the femoral head and hip stiffness. The purpose of this report was to describe a case with severe stiffness of the hip due to hypertonicity in periarticular muscles after it was treated for developmental dysplasia of the hip (DDH). PRESENTATION OF CASE Three-year-old patient referred to our institution with bilateral DDH. Two hips were operated separately in one year with anterior open reduction, femoral shortening osteotomy. Third month after last surgery, limited right hip range of motion and limb length discrepency identified. Clinical examination revealed that patient had limited range of motion (ROM) in the right hip and compensated this with pelvis obliquity. Gluteus medius, sartorius and iliofemoral band release performed after examination under general anesthesia. Symptoms were persisted at 3rd week control and examination of the patient in general anesthesia revealed full ROM without increased tension. For the identified hypertonicity, ultrasound guided 100IU botulinum toxin A injection performed to abductor group and iliopsoas muscles. Fifth month later, no flexor or abductor tension observed, and there was no pelvic obliquity. DISCUSSION Stiffness as a complication is rare and is usually resolved without treatment or simple physical therapy. Usually it is related with immobilization or surgery associated joint contracture, and spontaneous recovery reported. Presented case is diagnosed as hip stiffness due to underlying local hypertonicity. That is resolved with anesthesia and it was treated after using botulinum toxin A injection. CONCLUSION Hypertonicity with hip stiffness after surgical treatment of DDH differ from spontaneous recovering hip range of motion limitation and treatment can only be achieved by reduction of the muscle hypertonicity by neuromuscular junction blockage. PMID:24568944
Determination of reaeration coefficients for Ohio streams
Hren, Janet
1984-01-01
The hydrocarbon-gas tracer technique was used to determine reaeration coefficients on 30 reaches of Ohio streams. The studies were done from September 1979 through August 1982 to determine the reaeration coefficients for the individual reaches and to develop general equation that could be used to estimate the coefficients. Multiple linear regression was used to determine relationships among the reaeration coefficients and physical stream characteristics. Four special equation based on the general equation were developed from various combinations of discharge, slope, width, depth, measured velocity, and estimated velocity. The standard errors of estimate for these equations ranged from 37 to 47 percent. The variables that resulted in the lowest standard error of estimate were discharge, slope, width, depth, and measured velocity. The most significant variables were depth and velocity.
NASA Technical Reports Server (NTRS)
Childs, D. W.
1983-01-01
An improved theory for the prediction of the rotordynamic coefficients of turbulent annular seals was developed. Predictions from the theory are compared to the experimental results and an approach for the direct calculation of empirical turbulent coefficients from test data are introduced. An improved short seal solution is shown to do a better job of calculating effective stiffness and damping coefficients than either the original short seal solution or a finite length solution. However, the original short seal solution does a much better job of predicting equivalent added mass coefficient.
Permeability dependency on stiff and compliant porosities: a model and some experimental examples
NASA Astrophysics Data System (ADS)
Shapiro, S. A.; Khizhniak, G. P.; Plotnikov, V. V.; Niemann, R.; Ilyushin, P. Yu; Galkin, S. V.
2015-06-01
The relation between porosity and permeability is not unique. We show that stress dependencies of both porosity and permeability can provide useful information clarifying this relation. We propose that comparison of the functional dependency of porosity and permeability on stress shows which part of the void space in rocks controls the permeability, the compliant porosity or the stiff porosity. The compliant porosity (including very thin cracks and grain-contact vicinities) usually controls the stress dependencies of elastic moduli of rocks. One then observes exponential-like dependencies of elastic properties on effective stress. Stress-induced deformation of stiff pores (equant pores) have less significance for stress dependencies of elastic properties on loadings of low to moderate magnitudes (several tens of MPa). However, such pores can play a significant role in the stress dependency of permeability. We propose a rather general model of permeability as a function of the stiff and compliant porosity. The model includes the possibility that, in different rocks, permeability can be controlled by stiff pores or, alternatively, by compliant pores, or, finally, by a combination of these. This model predicts a functional dependency of permeability on stress, ranging from power-law to exponential-law and to a mixed behavior of permeability in these situations, respectively. We show experimental results for four samples of sedimentary rocks from oil reservoirs of the Russian Perm region indicating these types of behavior.
Evaluation of Compressive Strength and Stiffness of Grouted Soils by Using Elastic Waves
Lee, In-Mo; Kim, Jong-Sun; Yoon, Hyung-Koo; Lee, Jong-Sub
2014-01-01
Cement grouted soils, which consist of particulate soil media and cementation agents, have been widely used for the improvement of the strength and stiffness of weak ground and for the prevention of the leakage of ground water. The strength, elastic modulus, and Poisson's ratio of grouted soils have been determined by classical destructive methods. However, the performance of grouted soils depends on several parameters such as the distribution of particle size of the particulate soil media, grouting pressure, curing time, curing method, and ground water flow. In this study, elastic wave velocities are used to estimate the strength and elastic modulus, which are generally obtained by classical strength tests. Nondestructive tests by using elastic waves at small strain are conducted before and during classical strength tests at large strain. The test results are compared to identify correlations between the elastic wave velocity measured at small strain and strength and stiffness measured at large strain. The test results show that the strength and stiffness have exponential relationship with elastic wave velocities. This study demonstrates that nondestructive methods by using elastic waves may significantly improve the strength and stiffness evaluation processes of grouted soils. PMID:25025082
Evaluation of compressive strength and stiffness of grouted soils by using elastic waves.
Lee, In-Mo; Kim, Jong-Sun; Yoon, Hyung-Koo; Lee, Jong-Sub
2014-01-01
Cement grouted soils, which consist of particulate soil media and cementation agents, have been widely used for the improvement of the strength and stiffness of weak ground and for the prevention of the leakage of ground water. The strength, elastic modulus, and Poisson's ratio of grouted soils have been determined by classical destructive methods. However, the performance of grouted soils depends on several parameters such as the distribution of particle size of the particulate soil media, grouting pressure, curing time, curing method, and ground water flow. In this study, elastic wave velocities are used to estimate the strength and elastic modulus, which are generally obtained by classical strength tests. Nondestructive tests by using elastic waves at small strain are conducted before and during classical strength tests at large strain. The test results are compared to identify correlations between the elastic wave velocity measured at small strain and strength and stiffness measured at large strain. The test results show that the strength and stiffness have exponential relationship with elastic wave velocities. This study demonstrates that nondestructive methods by using elastic waves may significantly improve the strength and stiffness evaluation processes of grouted soils. PMID:25025082
A short note on the counter-intuitive spurious behaviors in stiff reacting flow
NASA Astrophysics Data System (ADS)
Zhang, Bin; Wang, Jian-Hang
2015-06-01
A well known spurious numerical phenomenon may occur in solving stiff detonation problems due to the under-resolved numerical solution in both space and time. Most people believe that decreasing numerical dissipation or stiffness will delay or eliminate the onset of spurious numerical phenomenon. However, several counter-intuitive spurious behaviors were observed by H.C. Yee et al. (2013) [10] recently and the mechanism of the generation of these strange phenomena remains an open question. The goal of this short note is to give a reasonable explanation for these counter-intuitive spurious behaviors existing in the detonation problems (the simplified 2 2 system and the reactive Euler equations) with stiff reacting source terms and discontinuities. In developing the mechanism of spurious numerical phenomenon in detonation problems, we find the parameters of the intermediate state are very important because they determine whether the spurious phenomenon will happen or not. Furthermore, these counter-intuitive spurious behaviors are mainly due to the oscillation of those intermediate state parameters as the time step or grid is refined gradually. These findings may help us to get a further understanding of some of the difficulties in numerical combustion and problems with stiff nonlinear source terms and discontinuities in general.
Vercher, Ana; Giner, Eugenio; Arango, Camila; Tarancn, Jos E; Fuenmayor, F Javier
2014-04-01
Mineralized collagen fibrils have been usually analyzed like a two-phase composite material where crystals are considered as platelets that constitute the reinforcement phase. Different models have been used to describe the elastic behavior of the material. In this work, it is shown that when Halpin-Tsai equations are applied to estimate elastic constants from typical constituent properties, not all crystal dimensions yield a model that satisfy thermodynamic restrictions. We provide the ranges of platelet dimensions that lead to positive definite stiffness matrices. On the other hand, a finite element model of a mineralized collagen fibril unit cell under periodic boundary conditions is analyzed. By applying six canonical load cases, homogenized stiffness matrices are numerically calculated. Results show a monoclinic behavior of the mineralized collagen fibril. In addition, a 5-layer lamellar structure is also considered where crystals rotate in adjacent layers of a lamella. The stiffness matrix of each layer is calculated applying Lekhnitskii transformations, and a new finite element model under periodic boundary conditions is analyzed to calculate the homogenized 3D anisotropic stiffness matrix of a unit cell of lamellar bone. Results are compared with the rule-of-mixtures showing in general good agreement. PMID:23793930
Mattei, Giorgio; Ferretti, Concetta; Tirella, Annalisa; Ahluwalia, Arti; Mattioli-Belmonte, Monica
2015-01-01
Bone extracellular matrix (ECM) is a natural composite made of collagen and mineral hydroxyapatite (HA). Dynamic cell-ECM interactions play a critical role in regulating cell differentiation and function. Understanding the principal ECM cues promoting osteogenic differentiation would be pivotal for both bone tissue engineering and regenerative medicine. Altering the mineral content generally modifies the stiffness as well as other physicochemical cues provided by composite materials, complicating the cause-effect analysis of resultant cell behaviour. To isolate the contribution of mechanical cues from other HA-derived signals, we developed and characterised composite HA/gelatin scaffolds with different mineral contents along with a set of stiffness-matched HA-free gelatin scaffolds. Samples were seeded with human periosteal derived progenitor cells (PDPCs) and cultured over 7 days, analysing their resultant morphology and gene expression. Our results show that both stiffness and HA contribute to directing PDPC osteogenic differentiation, highlighting the role of stiffness in triggering the expression of osteogenic genes and of HA in accelerating the process, particularly at high concentrations. PMID:26035412
Aortic Compliance and Stiffness Among Severe Longstanding Hypertensive and Non-hypertensive
Kamberi, Lulzim Selim; Gorani, Daut Rashit; Hoxha, Teuta Faik; Zahiti, Bedri Faik
2013-01-01
Introduction Abnormal aortic function in hypertension is generally attributed to accelerated breakdown of elastin in the aorta, leading to dilatation of the lumen and stiffening of the wall as elastin is replaced with stiffer collagen. Aortic stiffness is an independent predictor of cardiovascular risk and all-cause and cardiovascular mortality. Vascular stiffening can activate endothelium which in turn may promote atherogenesis. Modulation of arterial stiffness has been shown to be successfully managed via changes in lifestyle and put under control of hypertension pharmacologically with antihypertensive drugs and statins. Methods Hundred and forty four patients have been enrolled in this study. They have been divided in two groups, with hypertension and group of control. Groups were with no age difference. Results Group with hypertension were with reduced aortic strain, distensibility (compliance) and have higher stiffness than control group; GrHTA =9.3 compared to GC=5.4. After successful treatment of hypertension with antihypertensives and statins, for two years, these parameters showed improvement, but still remain out of normal range compared to control group; 7.6 vs. 5.38. Conclusions Hypertensive patients have reduced aortic elasticity and increased stiffness which can be stopped and improved after treatment with antihypertensive and statin. PMID:23572854
Effects of varying machine stiffness and contact area in UltraForm Finishing
NASA Astrophysics Data System (ADS)
Briggs, Dennis E.; Echaves, Samantha; Pidgeon, Brendan; Travis, Nathan; Ellis, Jonathan D.
2013-09-01
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.
Wang, Zhijie; Chesler, Naomi C.
2011-01-01
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. PMID:22034607
Pratt, Jon R.; Shaw, Gordon A.; Kumanchik, Lee; Burnham, Nancy A.
2010-02-15
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.
Dellimore, K; Kemp, I; Scheffer, C; Weich, H; Doubell, A
2013-12-01
Leaflet skin friction and stiffness were found to have a significant influence on the systolic performance of a 19 mm diameter bioprosthetic aortic valve based on fluid-structure interaction simulations at a heart rate of 72 bpm. Four different leaflet skin friction coefficients (0.0, 9.2 × 10(-4), 4.8 × 10(-2) and 4.8 × 10(-1)) were simulated along with three different leaflet elastic moduli (3.0 × 10(6), 3.5 × 10(6), 4.0 × 10(6) N m(-2)). Higher leaflet skin friction was found to increase the magnitude of the systolic transvalvular pressure gradient and the peak velocity through the valve, as well as decrease the valve orifice area. The results for the leaflet opening and closing kinematics also showed that higher leaflet skin friction combined with higher leaflet stiffness produces longer rapid valve opening, closing and ejection times, as well as smaller valve orifice areas. These results are consistent with clinical findings for calcified aortic valves and suggest that valve performance under stenotic conditions is strongly influenced by the combined effect of increasing leaflet stiffness and surface roughness caused by calcification. PMID:24264225
Mechanically stiff, electrically conductive composites of polymers and carbon nanotubes
Worsley, Marcus A.; Kucheyev, Sergei O.; Baumann, Theodore F.; Kuntz, Joshua D.; Satcher, Jr., Joe H.; Hamza, Alex V.
2015-07-21
Using SWNT-CA as scaffolds to fabricate stiff, highly conductive polymer (PDMS) composites. The SWNT-CA is immersing in a polymer resin to produce a SWNT-CA infiltrated with a polymer resin. The SWNT-CA infiltrated with a polymer resin is cured to produce the stiff and electrically conductive composite of carbon nanotube aerogel and polymer.
Boundary Stiffness Regulates Fibroblast Behavior in Collagen Gels
John, Jeffrey; Quinlan, Angela Throm; Silvestri, Chiara; Billiar, Kristen
2010-01-01
Recent studies have illustrated the profound dependence of cellular behavior on the stiffness of 2D culture substrates. The goal of this study was to develop a method to alter the stiffness cells experience in a standard 3D collagen gel model without affecting the physiochemical properties of the extracellular matrix. A device was developed utilizing compliant anchors (0.0480.64 N m?1) to tune the boundary stiffness of suspended collagen gels in between the commonly utilized free and fixed conditions (zero and infinite stiffness boundary stiffness). We demonstrate the principle of operation with finite element analyses and a wide range of experimental studies. In all cases, boundary stiffness has a strong influence on cell behavior, most notably eliciting higher basal tension and activated force (in response to KCl) and more pronounced remodeling of the collagen matrix at higher boundary stiffness levels. Measured equibiaxial forces for gels seeded with 3 million human foreskin fibroblasts range from 0.05 to 1 mN increasing monotonically with boundary stiffness. Estimated force per cell ranges from 17 to 100 nN utilizing representative volume element analysis. This device provides a valuable tool to independently study the effect of the mechanical environment of the cell in a 3D collagen matrix. PMID:20012205
Intra-abdominal pressure increases stiffness of the lumbar spine.
Hodges, Paul W; Eriksson, A E Martin; Shirley, Debra; Gandevia, Simon C
2005-09-01
Intra-abdominal pressure (IAP) increases during many tasks and has been argued to increase stability and stiffness of the spine. Although several studies have shown a relationship between the IAP increase and spinal stability, it has been impossible to determine whether this augmentation of mechanical support for the spine is due to the increase in IAP or the abdominal muscle activity which contributes to it. The present study determined whether spinal stiffness increased when IAP increased without concurrent activity of the abdominal and back extensor muscles. A sustained increase in IAP was evoked by tetanic stimulation of the phrenic nerves either unilaterally or bilaterally at 20 Hz (for 5 s) via percutaneous electrodes in three subjects. Spinal stiffness was measured as the force required to displace an indentor over the L4 or L2 spinous process with the subjects lying prone. Stiffness was measured as the slope of the regression line fitted to the linear region of the force-displacement curve. Tetanic stimulation of the diaphragm increased IAP by 27-61% of a maximal voluntary pressure increase and increased the stiffness of the spine by 8-31% of resting levels. The increase in spinal stiffness was positively correlated with the size of the IAP increase. IAP increased stiffness at L2 and L4 level. The results of this study provide evidence that the stiffness of the lumbar spine is increased when IAP is elevated. PMID:16023475
An experimental nonlinear low dynamic stiffness device for shock isolation
NASA Astrophysics Data System (ADS)
Francisco Ledezma-Ramirez, Diego; Ferguson, Neil S.; Brennan, Michael J.; Tang, Bin
2015-07-01
The problem of shock generated vibration is very common in practice and difficult to isolate due to the high levels of excitation involved and its transient nature. If not properly isolated it could lead to large transmitted forces and displacements. Typically, classical shock isolation relies on the use of passive stiffness elements to absorb energy by deformation and some damping mechanism to dissipate residual vibration. The approach of using nonlinear stiffness elements is explored in this paper, focusing in providing an isolation system with low dynamic stiffness. The possibilities of using such a configuration for a shock mount are studied experimentally following previous theoretical models. The model studied considers electromagnets and permanent magnets in order to obtain nonlinear stiffness forces using different voltage configurations. It is found that the stiffness nonlinearities could be advantageous in improving shock isolation in terms of absolute displacement and acceleration response when compared with linear elastic elements.
Convergent-tapered annular seals - Analysis and testing for rotordynamic coefficients
NASA Technical Reports Server (NTRS)
Childs, D. W.; Dressman, J. B.
1984-01-01
A combined analytical-computational method has been developed to calculate the pressure field and dynamic coefficients for tapered high-pressure annular seals. Completely developed turbulent flow is assumed in both the circumferential and axial directions, according to Hirs' (1973) bulk-flow turbulent-lubrication equations. In a numerical experiment with the method, a short bearing approximation is used to derive an analytical expression for the first-order (dynamic) pressure gradient. This expression is integrated numerically to define dynamic coefficients of the seal. Numerical results of the integration are compared with previous results for straight and tapered seals. It is found that direct stiffness and leakage coefficients increase in the present seal, while the remaining coefficients decrease. An optimal taper angle is shown to exist with respect to: (1) the direct stiffness and (2) the ratio of direct stiffness to leakage. On the basis of the optimal taper angle calculations, stiffness increases on the order of 40 to 50 percent are predicted. Experimental results for three taper angles are presented, and are found to be in good agreement with the theoretical predictions.
The Focal Adhesion: A Regulated Component of Aortic Stiffness
Saphirstein, Robert J.; Gao, Yuan Z.; Jensen, Mikkel H.; Gallant, Cynthia M.; Vetterkind, Susanne; Moore, Jeffrey R.; Morgan, Kathleen G.
2013-01-01
Increased aortic stiffness is an acknowledged predictor and cause of cardiovascular disease. The sources and mechanisms of vascular stiffness are not well understood, although the extracellular matrix (ECM) has been assumed to be a major component. We tested here the hypothesis that the focal adhesions (FAs) connecting the cortical cytoskeleton of vascular smooth muscle cells (VSMCs) to the matrix in the aortic wall are a component of aortic stiffness and that this component is dynamically regulated. First, we examined a model system in which magnetic tweezers could be used to monitor cellular cortical stiffness, serum-starved A7r5 aortic smooth muscle cells. Lysophosphatidic acid (LPA), an activator of myosin that increases cell contractility, increased cortical stiffness. A small molecule inhibitor of Src-dependent FA recycling, PP2, was found to significantly inhibit LPA-induced increases in cortical stiffness, as well as tension-induced increases in FA size. To directly test the applicability of these results to force and stiffness development at the level of vascular tissue, we monitored mouse aorta ring stiffness with small sinusoidal length oscillations during agonist-induced contraction. The alpha-agonist phenylephrine, which also increases myosin activation and contractility, increased tissue stress and stiffness in a PP2- and FAK inhibitor 14-attenuated manner. Subsequent phosphotyrosine screening and follow-up with phosphosite-specific antibodies confirmed that the effects of PP2 and FAK inhibitor 14 in vascular tissue involve FA proteins, including FAK, CAS, and paxillin. Thus, in the present study we identify, for the first time, the FA of the VSMC, in particular the FAK-Src signaling complex, as a significant subcellular regulator of aortic stiffness and stress. PMID:23626821
Leg stiffness adjustment during hopping at different intensities and frequencies.
Mrdakovic, Vladimir; Ilic, Dusko; Vulovic, Radun; Matic, Milan; Jankovic, Nenad; Filipovic, Nenad
2014-01-01
Understanding leg and joint stiffness adjustment during maximum hopping may provide important information for developing more effective training methods. It has been reported that ankle stiffness has major influence on stable spring-mass dynamics during submaximal hopping, and that knee stiffness is a major determinant for hopping performance during maximal hopping task. Furthermore, there are no reports on how the height of the previous hop could affect overall stiffness modulation of the subsequent maximum one. The purpose of the present study was to determine whether and how the jump height of the previous hop affects leg and joint stiffness for subsequent maximum hop. Ten participants completed trials in which they repeatedly hopped as high as possible (MX task) and trials in which they were instructed to perform several maximum hops with 3 preferred (optimal) height hops between each of them (P3MX task). Both hopping tasks were performed at 2.2 Hz hopping frequency and at the participant's preferred (freely chosen) frequency as well. By comparing results of those hopping tasks, we found that ankle stiffness at 2.2 Hz ( p = 0.041) and knee stiffness at preferred frequency ( p = 0.045) was significantly greater for MX versus P3MX tasks. Leg stiffness for 2.2 Hz hopping is greater than for the preferred frequency. Ankle stiffness is greater for 2.2 Hz than for preferred frequencies; opposite stands for knee stiffness. The results of this study suggest that preparatory hop height can be considered as an important factor for modulation of maximum hop. PMID:25308379
Increased central arterial stiffness in hypothyroidism.
Obuobie, K; Smith, J; Evans, L M; John, R; Davies, J S; Lazarus, J H
2002-10-01
Hypothyroidism is associated with cardiovascular dysfunction. It is increasingly apparent that stiffening of central arteries may lead to increased afterload and cardiac dysfunction. We noninvasively studied the peripheral and central pressure waveforms in 12 untreated hypothyroid patients as well as in 12 age-, sex-, and body mass index-matched controls using the technique of pulse wave analysis from recordings at the radial artery. Indexes of arterial stiffness, augmentation index (AI) and augmentation of central arterial pressure (AG), were derived as well as time of travel of the reflected wave (TR), a direct estimate of aortic pulse wave velocity. At baseline, there were no significant differences between the 2 groups in brachial and aortic blood pressures. Hypothyroid patients had significantly higher AI than controls (mean +/- SEM[SCAP], 32.0 +/- 3.4% vs. 17.0 +/- 2.4%; P < 0.0005) even when corrected for heart rate (AI(C); 28.0 +/- 3.2% vs. 17.0 +/- 2.4%; P < 0.006) and AG (13.0 +/- 2.2 vs. 7.0 +/- 2.1 mm Hg; P < 0.03) together with a lower TR (132.0 +/- 4.1 vs. 142.0 +/- 1.5 msec; P < 0.03). After 6 months of therapy with T(4), all patients were euthyroid. AI(C) had decreased in the patient group (23.0 +/- 3.2% vs. 28.0 +/- 3.2%; P < 0.01) as had AG (9.0 +/- 1.5 vs. 13.0 +/- 2.2 mm Hg; P < 0.008), but TR was significantly higher (142.0 +/- 3.0 vs. 132.0 +/- 4.1 msec; P < 0.008). AI correlated with age in all groups (hypothyroid group: r = 0.937; P < 0.0005; control group: r = 0.804; P < 0.0005), but correlated with TSH level only among controls (r = 0.591; P < 0.05). This study confirms that hypothyroidism is associated with increased cardiovascular risk, as evidenced by increased augmentation of central aortic pressures and central arterial stiffness. Furthermore, these abnormalities are reversed after adequate T(4) replacement. PMID:12364455
Stiffness characteristics of airfoils under pulse loading
NASA Astrophysics Data System (ADS)
Turner, Kevin Eugene
The turbomachinery industry continually struggles with the adverse effects of contact rubs between airfoils and casings. The key parameter controlling the severity of a given rub event is the contact load produced when the airfoil tips incur into the casing. These highly non-linear and transient forces are difficult to calculate and their effects on the static and rotating components are not well understood. To help provide this insight, experimental and analytical capabilities have been established and exercised through an alliance between GE Aviation and The Ohio State University Gas Turbine Laboratory. One of the early findings of the program is the influence of blade flexibility on the physics of rub events. The core focus of the work presented in this dissertation is to quantify the influence of airfoil flexibility through a novel modeling approach that is based on the relationship between applied force duration and maximum tip deflection. This relationship is initially established using a series of forward, non-linear and transient analyses in which simulated impulse rub loads are applied. This procedure, although effective, is highly inefficient and costly to conduct by requiring numerous explicit simulations. To alleviate this issue, a simplified model, named the pulse magnification model, is developed that only requires a modal analysis and a static analyses to fully describe how the airfoil stiffness changes with respect to load duration. Results from the pulse magnification model are compared to results from the full transient simulation method and to experimental results, providing sound verification for the use of the modeling approach. Furthermore, a unique and highly efficient method to model airfoil geometries was developed and is outlined in this dissertation. This method produces quality Finite Element airfoil definitions directly from a fully parameterized mathematical model. The effectiveness of this approach is demonstrated by comparing modal properties of the simulated geometries to modal properties of various current airfoil designs. Finally, this modeling approach was used in conjunction with the pulse magnification model to study the effects of various airfoil geometric features on the stiffness of the blade under impulsive loading.
Bo, L.; Waugh, R. E.
1989-01-01
The curvature elastic modulus (bending stiffness) of stearoyloleoyl phosphatidylcholine (SOPC) bilayer membrane is determined from membrane tether formation experiments. R. E. Waugh and R. M. Hochmuth 1987. Biophys. J. 52:391-400) have shown that the radius of a bilayer cylinder (tether) is inversely related to the force supported along its axis. The coefficient that relates the axial force on the tether to the tether radius is the membrane bending stiffness. Thus, the bending stiffness can be calculated directly from measurements of the tether radius as a function of force. Giant (10-50-microns diam) thin-walled vesicles were aspirated into a micropipette and a tether was pulled out of the surface by gravitational forces on small glass beads that had adhered to the vesicle surface. Because the vesicle keeps constant surface area and volume, formation of the tether requires displacement of material from the projection of the vesicle in the pipette. Tethers can be made to grow longer or shorter or to maintain equilibrium by adjusting the aspiration pressure in the micropipette at constant tether force. The ratio of the change in the length of the tether to the change in the projection length is proportional to the ratio of the pipette radius to the tether radius. Thus, knowing the density and diameter of the glass beads and measuring the displacement of the projection as a function of tether length, independent determinations of the force on the tether and the tether radius were obtained. The bending stiffness for an SOPC bilayer obtained from these data is approximately 2.0 x 10(-12) dyn cm, for tether radii in the range of 20-100 nm. An equilibrium relationship between pressure and tether force is derived which closely matches experimental observation. Images FIGURE 4 p512-b PMID:2930831
Passive mechanical models of fish caudal fins: effects of shape and stiffness on self-propulsion.
Feilich, Kara L; Lauder, George V
2015-06-01
Fishes are found in a great variety of body forms with tail shapes that vary from forked tuna-like tails to the square-shaped tails found in some deep-bodied species. Hydrodynamic theory suggests that a fish's body and tail shape affects undulatory swimming performance. For example, a narrow caudal peduncle is believed to reduce drag, and a tuna-like tail to increase thrust. Despite the prevalence of these assertions, there is no experimental verification of the hydrodynamic mechanisms that may confer advantages on specific forms. Here, we use a mechanically-actuated flapping foil model to study how two aspects of shape, caudal peduncle depth and presence or absence of a forked caudal fin, may affect different aspects of swimming performance. Four different foil shapes were each made of plastics of three different flexural stiffnesses, permitting us to study how shape might interact with stiffness to produce swimming performance. For each foil, we measured the self-propelling swimming speed. In addition, we measured the forces, torques, cost of transport and power coefficient of each foil swimming at its self-propelling speed. There was no single 'optimal' foil exhibiting the highest performance in all metrics, and for almost all measures of swimming performance, foil shape and flexural stiffness interacted in complicated ways. Particle image velocimetry of several foils suggested that stiffness might affect the relative phasing of the body trailing edge and the caudal fin leading edge, changing the flow incident to the tail, and affecting hydrodynamics of the entire foil. The results of this study of a simplified model of fish body and tail morphology suggest that considerable caution should be used when inferring a swimming performance advantage from body and tail shape alone. PMID:25879846
Controlled Unusual Stiffness of Mechanical Metamaterials.
Lee, Wooju; Kang, Da-Young; Song, Jihwan; Moon, Jun Hyuk; Kim, Dongchoul
2016-01-01
Mechanical metamaterials that are engineered with sub-unit structures present unusual mechanical properties depending on the loading direction. Although they show promise, their practical utility has so far been somewhat limited because, to the best of our knowledge, no study about the potential of mechanical metamaterials made from sophisticatedly tailored sub-unit structures has been made. Here, we present a mechanical metamaterial whose mechanical properties can be systematically designed without changing its chemical composition or weight. We study the mechanical properties of triply periodic bicontinuous structures whose detailed sub-unit structure can be precisely fabricated using various sub-micron fabrication methods. Simulation results show that the effective wave velocity of the structures along with different directions can be designed to introduce the anisotropy of stiffness by changing a volume fraction and aspect ratio. The ratio of Young's modulus to shear modulus can be increased by up to at least 100, which is a 3500% increase over that of isotropic material (2.8, acrylonitrile butadiene styrene). Furthermore, Poisson's ratio of the constituent material changes the ratio while Young's modulus does not influence it. This study presents the promising potential of mechanical metamaterials for versatile industrial and biomedical applications. PMID:26837466
Controlled Unusual Stiffness of Mechanical Metamaterials
Lee, Wooju; Kang, Da-Young; Song, Jihwan; Moon, Jun Hyuk; Kim, Dongchoul
2016-01-01
Mechanical metamaterials that are engineered with sub-unit structures present unusual mechanical properties depending on the loading direction. Although they show promise, their practical utility has so far been somewhat limited because, to the best of our knowledge, no study about the potential of mechanical metamaterials made from sophisticatedly tailored sub-unit structures has been made. Here, we present a mechanical metamaterial whose mechanical properties can be systematically designed without changing its chemical composition or weight. We study the mechanical properties of triply periodic bicontinuous structures whose detailed sub-unit structure can be precisely fabricated using various sub-micron fabrication methods. Simulation results show that the effective wave velocity of the structures along with different directions can be designed to introduce the anisotropy of stiffness by changing a volume fraction and aspect ratio. The ratio of Young’s modulus to shear modulus can be increased by up to at least 100, which is a 3500% increase over that of isotropic material (2.8, acrylonitrile butadiene styrene). Furthermore, Poisson’s ratio of the constituent material changes the ratio while Young’s modulus does not influence it. This study presents the promising potential of mechanical metamaterials for versatile industrial and biomedical applications. PMID:26837466
Controlled Unusual Stiffness of Mechanical Metamaterials
NASA Astrophysics Data System (ADS)
Lee, Wooju; Kang, Da-Young; Song, Jihwan; Moon, Jun Hyuk; Kim, Dongchoul
2016-02-01
Mechanical metamaterials that are engineered with sub-unit structures present unusual mechanical properties depending on the loading direction. Although they show promise, their practical utility has so far been somewhat limited because, to the best of our knowledge, no study about the potential of mechanical metamaterials made from sophisticatedly tailored sub-unit structures has been made. Here, we present a mechanical metamaterial whose mechanical properties can be systematically designed without changing its chemical composition or weight. We study the mechanical properties of triply periodic bicontinuous structures whose detailed sub-unit structure can be precisely fabricated using various sub-micron fabrication methods. Simulation results show that the effective wave velocity of the structures along with different directions can be designed to introduce the anisotropy of stiffness by changing a volume fraction and aspect ratio. The ratio of Young’s modulus to shear modulus can be increased by up to at least 100, which is a 3500% increase over that of isotropic material (2.8, acrylonitrile butadiene styrene). Furthermore, Poisson’s ratio of the constituent material changes the ratio while Young’s modulus does not influence it. This study presents the promising potential of mechanical metamaterials for versatile industrial and biomedical applications.
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.
2011-01-01
A survey of studies conducted since 1914 on the use of equivalent-plate stiffnesses in modeling the overall, stiffness-critical response of stiffened plates and shells is presented. Two detailed, comprehensive derivations of first-approximation equivalent-plate stiffnesses are also presented that are based on the Reissner-Mindlin-type, first-order transverse-shear deformation theory for anisotropic plates. Equivalent-plate stiffness expressions, and a corresponding symbolic manipulation computer program, are also presented for several different stiffener configurations. These expressions are very general and exhibit the full range of anisotropies permitted by the Reissner-Mindlin-type, first-order transverse-shear deformation theory for anisotropic plates. The expressions presented in the present study were also compared with available, previously published results. For the most part, the previously published results are for special cases of the general expressions presented herein and are almost in complete agreement. Analysis is also presented that extends the use of the equivalent-plate stiffness expressions to sandwich plates.
2014-01-01
Introduction Mixed cryoglobulinemia (MC) is a HCV-related lymphoproliferative disorder generally associated with advanced liver disease. Liver stiffness has been significantly correlated with histopathological stage of fibrosis. Moreover, it was influenced by necroinflammatory activity. Rituximab (RTX) is a chimeric anti-CD20 monoclonal antibody inducing transient B lymphocytes depletion that was shown to be useful and safe in the majority of HCV MC patients, leading also to improvement of cirrhotic syndrome. Aim of this study was to evaluate the modifications of liver stiffness following RTX treatment in HCV-related MC patients. Materials and methods Fourteen consecutive patients (10 F, 4 M; mean age 60.43 ± 43) with HCV-related chronic hepatitis (n = 10) or cirrhosis (n = 4) and MC, eligible for RTX treatment, were prospectively enrolled. Intravenous injection of 1 g of RTX was performed at day 0 and at day 15. Assessment of stiffness was carried out by Fibroscan® (Echosens, Paris-France) at baseline, 15 days after the first infusion, and at month 1, 3 and 6 after therapy. Results MC symptoms significantly improved during the study, especially during the first 3 months. Liver stiffness observed 3 months after treatment was significantly reduced when compared with pre-treatment values (p = 0.01). This difference disappeared after 6 months of follow-up. Cytofluorimetric analysis showed a decrease of CD19+ peripheral blood cells, with the nadir at month 3 after therapy and B cell compartment reconstitution after 6 months. Conclusion This study, for the first time showed that RTX-treatment in HCV-related MC induces a reduction of liver stiffness that is strictly associated with the B-cell depletion. PMID:24456582
NASA Astrophysics Data System (ADS)
Wang, X.; Zheng, G. T.
2016-02-01
A simple and general Equivalent Dynamic Stiffness Mapping technique is proposed for identifying the parameters or the mathematical model of a nonlinear structural element with steady-state primary harmonic frequency response functions (FRFs). The Equivalent Dynamic Stiffness is defined as the complex ratio between the internal force and the displacement response of unknown element. Obtained with the test data of responses' frequencies and amplitudes, the real and imaginary part of Equivalent Dynamic Stiffness are plotted as discrete points in a three dimensional space over the displacement amplitude and the frequency, which are called the real and the imaginary Equivalent Dynamic Stiffness map, respectively. These points will form a repeatable surface as the Equivalent Dynamic stiffness is only a function of the corresponding data as derived in the paper. The mathematical model of the unknown element can then be obtained by surface-fitting these points with special functions selected by priori knowledge of the nonlinear type or with ordinary polynomials if the type of nonlinearity is not pre-known. An important merit of this technique is its capability of dealing with strong nonlinearities owning complicated frequency response behaviors such as jumps and breaks in resonance curves. In addition, this technique could also greatly simplify the test procedure. Besides there is no need to pre-identify the underlying linear parameters, the method uses the measured data of excitation forces and responses without requiring a strict control of the excitation force during the test. The proposed technique is demonstrated and validated with four classical single-degree-of-freedom (SDOF) numerical examples and one experimental example. An application of this technique for identification of nonlinearity from multiple-degree-of-freedom (MDOF) systems is also illustrated.
Comparison of the acute impact of maximal arm and leg aerobic exercise on arterial stiffness.
Ranadive, S M; Fahs, C A; Yan, H; Rossow, L M; Agiovlasitis, S; Fernhall, B
2012-07-01
Acute aerobic exercise decreases arterial stiffness based on the intensity of the exercise and the arterial segment studied. Arm exercise may differentially affect arterial stiffness compared to leg exercise but this has not been studied. We hypothesized that maximal aerobic exercise would reduce local peripheral pulse wave velocity i.e. femoral-dorsalis pedis (LPWV) following leg exercise and carotid-radial (APWV) following arm exercise without any crossover effect. The main purpose of the study is to compare the effects of maximal arm versus leg aerobic exercise on peripheral and central arterial stiffness. Fifteen healthy participants (9 males and 6 females, 25 5 years) performed maximal arm-ergometer and leg-ergometer exercise in a randomized, crossover design. Peripheral and central pulse wave velocities (PWV) were obtained using applanation tonometry before and 10 min after each maximal exercise bout. 2 2 repeated measures analysis of variance was used to detect differences between conditions. There was a significant interaction in the APWV between the two exercise modes. However, there was no condition or interaction effect on LPWV following maximal arm versus leg exercise. There was no significant difference in central PWV between conditions or with time. There was no change in MAP (75 6-77 3) after maximal arm exercise as compared to the maximal leg exercise (73 6-80 2). Arm exercise produced a more generalized effect on arterial stiffness than leg exercise. The prescription of upper limb exercise may be considered for purposes of eliciting post-exercise systemic changes in arterial stiffness. PMID:22083536
Stability analysis and backward whirl investigation of cracked rotors with time-varying stiffness
NASA Astrophysics Data System (ADS)
AL-Shudeifat, Mohammad A.
2015-07-01
The dynamic stability of dynamical systems with time-periodic stiffness is addressed here. Cracked rotor systems with time-periodic stiffness are well-known examples of such systems. Time-varying area moments of inertia at the cracked element cross-section of a cracked rotor have been used to formulate the time-periodic finite element stiffness matrix. The semi-infinite coefficient matrix obtained by applying the harmonic balance (HB) solution to the finite element (FE) equations of motion is employed here to study the dynamic stability of the system. Consequently, the sign of the determinant of a scaled version of a sub-matrix of this semi-infinite coefficient matrix at a finite number of harmonics in the HB solution is found to be sufficient for identifying the major unstable zones of the system in the parameter plane. Specifically, it is found that the negative determinant always corresponds to unstable zones in all of the systems considered. This approach is applied to a parametrically excited Mathieu's equation, a two degree-of-freedom linear time-periodic dynamical system, a cracked Jeffcott rotor and a finite element model of the cracked rotor system. Compared to the corresponding results obtained by Floquet's theory, the sign of the determinant of the scaled sub-matrix is found to be an efficient tool for identifying the major unstable zones of the linear time-periodic parametrically excited systems, especially large-scale FE systems. Moreover, it is found that the unstable zones for a FE cracked rotor with an open transverse crack model only appear at the backward whirl. The theoretical and experimental results have been found to agree well for verifying that the open crack model excites the backward whirl amplitudes at the critical backward whirling rotational speeds.
akar, Mustafa; Balta, ?evket; ?arlak, Hakan; Akhan, Muharrem; Demirkol, Sait; Karaman, Murat; Ay, Seyit Ahmet; Kurt, mer; ayci, Tuncer; ?nal, Sat?lm??; Demirba?, ?eref
2015-10-01
ObjectiveThere is a growing body of data supporting the association between diabetes and microcirculatory disfunction. We aimed to study e-selectin levels, and their associations with serum markers of inflammation and arterial stiffness in prediabetes and newly diagnosed diabetes patients in this study.Subjects and methodsSixty patients (25 females) with a newly established elevated fasting serum glucose [20 impaired fasting glucose (IFG), 20 impaired glucose tolerance (IGT), 20 newly diagnosed diabetes (T2DM)] and 17 healthy controls (13 females) were included in the study. Serum e-selectin and hs-CRP levels, and arterial stiffness parameters of the patients were studied.ResultsFasting serum glucose was the most important predictor of serum e-selectin levels. Pulse wave velocity and central aortic pressures were significantly higher in IFG, IGT and T2DM groups, compared to controls (p = 0.001, < 0.001, 0.013 and 0.015, 0.002, 0.009, respectively). The mean arterial pressure did not show any significant association with serum e-selectin and hs-CRP levels (? coefficient: 0.092, p = 0.358; and ? coefficient: 0.189, p = 0.362, respectively).ConclusionPrediabetes patients have increasing e-selectin levels through the diagnosis of T2DM. E-selectin is associated with serum glucose levels. Prediabetic and newly diagnosed diabetics have higher arterial stiffness measurements. Serum e-selectin may be a good marker of endothelial inflammation and dysfunction increasing in parallel with serum glucose levels, predicting future cardiovascular events. PMID:26201008
Arterial Stiffness, Distensibility, and Strain in Asthmatic Children
Özkan, Esra Akyüz; Serin, Halil İbrahim; Khosroshahi, Hashem E.; Kılıç, Mahmut; Ekim, Meral; Beysel, Perihan; Geçit, U. Aliye; Domur, Esra
2016-01-01
Background We hypothesized that since asthma is a chronic inflammatory disease, it could lead to the early development of atherosclerosis in childhood-onset asthma. The aim of this study was to investigate arterial stiffness, distensibility, and strain of different peripheral arteries, the parameters of which can be used to detect atherosclerosis in asthmatic children. Material/Methods We studied 22 pediatric patients with asthma and 18 healthy children. Fasting blood glucose and cholesterol levels were evaluated to exclude children with diabetes and hyperlipidemia, which are risk factors for atherosclerosis. Renal, carotid, and brachial arteries diameters were measured. Using the measured data, stiffness, distensibility, and strain of the arteries of all children were calculated. Results Pulse pressure, systolic and diastolic blood pressure, heart rate, cholesterols, and glucose levels of the obese individuals were similar to the controls. In carotid arteries there were no statistical differences regarding stiffness, distensibility, and strain. According to multiple ANCOVA analysis, distensibility and strain of right and left brachial arteries and right renal artery were higher, whereas right renal artery stiffness was lower in asthmatic children than in controls. Approximately one-fifth of the change in the left and right brachial arteries and right renal artery distensibility and strain and a small portion of the change in the right renal artery stiffness were associated with asthma. In contrast, left renal artery distensibility, strain, and stiffness were not associated with asthma. Conclusions Peripheral arteries had higher distensibility and strain, and lower stiffness in asthmatic children than in controls. PMID:26803723
Arterial stiffness and cognitive function in the elderly
Hazzouri, Adina Zeki Al; Yaffe, Kristine
2015-01-01
Cognitive decline and dementia are a major cause of disability and mortality among older adults. Cross-sectional evidence from observational studies suggests that greater arterial stiffness is associated with worse cognitive performance. These associations have been observed on measures of global cognition and across multiple domains of cognition. Epidemiologic evidence on the association between arterial stiffness and rate of cognitive decline has been less definitive, and very few studies have investigated the risk of developing dementia. This review summarizes the current research on arterial stiffness and cognition, issues around measurement and the effect that potential intervention might have on the course of cognitive aging. The evidence on pharmacological and non-pharmacological (exercise, nutrition, etc) interventions in older adults with arterial stiffness is promising. Yet there are no studies or trials that directly evaluate how interventions of arterial stiffness reduce or prevent cognitive impairment and risk of developing dementia. More research is needed to elucidate the causal link between arterial stiffness and cognitive decline and dementia, and to identify whether potential interventions to prevent or reduce arterial stiffness may benefit cognitive health of the elderly. PMID:25351110
Management of the Stiff Finger: Evidence and Outcomes
Yang, Guang; McGlinn, Evan P.; Chung, Kevin C.
2014-01-01
SYNOPSIS The term stiff finger refers to a reduction in the range of motion in the finger, and it is a condition that has many different causes and involves a number of different structures. Almost all injuries of the fingers and some diseases can cause finger stiffness. Hand surgeons often face difficulty treating stiff fingers that are affected by irreversible soft tissues fibrosis. Stiff fingers can be divided into flexion and extension deformities. They can also be sub-classified into four categories according to the involved tissues extending from the skin to the joint capsule. Prevention of stiff fingers by judicious mobilization of the joints is prudent to avoid more complicated treatment after established stiffness occurs. Static progressive and dynamic splints have been considered as effective non-operative interventions to treat stiff fingers. Most authors believe force of joint distraction and time duration of stretching are two important factors to consider while applying a splint or cast. We also introduce the concepts of capsulotomy and collateral ligament release and other soft tissue release of the MCP and PIP joint in this article. Future outcomes research is vital to assessing the effectiveness of these surgical procedures and guiding postoperative treatment recommendations. PMID:24996467
Effect of ECM Stiffness on Integrin-Ligand Binding Strength
NASA Astrophysics Data System (ADS)
Thomas, Gawain; Wen, Qi
2014-03-01
Many studies have shown that cells respond to the stiffness of their extracellular matrix (ECM). However, the mechanism of this stiffness sensing is not fully understood. We believe that cells probe stiffness by applying intracellular force to the ECM via the integrin-mediated adhesions. The linkage of integrins to the cytoskeleton has been modeled as a slip clutch, which has been shown to affect focal adhesion formation and hence force transmission in a stiffness dependent manner. In contrast, the bonds between integrins and ECM have been characterized as ``catch bonds.'' It is unclear how ECM viscoelasticity affects these catch bonds. We report, for the first time, the effects of ECM stiffness on the binding strength of integrins to ECM ligands by measuring the rupture force of individual integrin-ligand bonds of cells on collagen-coated polyacrylamide gels. Results show that the integrin-collagen bonds of 3T3 fibroblasts are nearly four times stronger on a stiff (30 kPa) gel than on a soft (3 kPa) gel. The stronger integrin bonds on stiffer substrates can promote focal adhesion formation. This suggests that the substrate stiffness regulates the cell-ECM adhesions not only by affecting the cytoskeleton-integrin links but also by modulating the binding of integrins to the ECM.
Arterial Stiffness, Distensibility, and Strain in Asthmatic Children.
Akyz zkan, Esra; Serin, Halil ?brahim; Khosroshahi, Hashem E; K?l?, Mahmut; Ekim, Meral; Beysel, Perihan; Geit, U Aliye; Domur, Esra
2016-01-01
BACKGROUND We hypothesized that since asthma is a chronic inflammatory disease, it could lead to the early development of atherosclerosis in childhood-onset asthma. The aim of this study was to investigate arterial stiffness, distensibility, and strain of different peripheral arteries, the parameters of which can be used to detect atherosclerosis in asthmatic children. MATERIAL AND METHODS We studied 22 pediatric patients with asthma and 18 healthy children. Fasting blood glucose and cholesterol levels were evaluated to exclude children with diabetes and hyperlipidemia, which are risk factors for atherosclerosis. Renal, carotid, and brachial arteries diameters were measured. Using the measured data, stiffness, distensibility, and strain of the arteries of all children were calculated. RESULTS Pulse pressure, systolic and diastolic blood pressure, heart rate, cholesterols, and glucose levels of the obese individuals were similar to the controls. In carotid arteries there were no statistical differences regarding stiffness, distensibility, and strain. According to multiple ANCOVA analysis, distensibility and strain of right and left brachial arteries and right renal artery were higher, whereas right renal artery stiffness was lower in asthmatic children than in controls. Approximately one-fifth of the change in the left and right brachial arteries and right renal artery distensibility and strain and a small portion of the change in the right renal artery stiffness were associated with asthma. In contrast, left renal artery distensibility, strain, and stiffness were not associated with asthma. CONCLUSIONS Peripheral arteries had higher distensibility and strain, and lower stiffness in asthmatic children than in controls. PMID:26803723
Mechanically Stiff Nanocomposite Hydrogels at Ultralow Nanoparticle Content.
Jaiswal, Manish K; Xavier, Janet R; Carrow, James K; Desai, Prachi; Alge, Daniel; Gaharwar, Akhilesh K
2016-01-26
Although hydrogels are able to mimic native tissue microenvironments, their utility for biomedical applications is severely hampered due to limited mechanical stiffness and low toughness. Despite recent progress in designing stiff and tough hydrogels, it is still challenging to achieve a cell-friendly, high modulus construct. Here, we report a highly efficient method to reinforce collagen-based hydrogels using extremely low concentrations of a nanoparticulate-reinforcing agent that acts as a cross-link epicenter. Extraordinarily, the addition of these nanoparticles at a 10?000-fold lower concentration relative to polymer resulted in a more than 10-fold increase in mechanical stiffness and a 20-fold increase in toughness. We attribute the high stiffness of the nanocomposite network to the chemical functionality of the nanoparticles, which enabled the cross-linking of multiple polymeric chains to the nanoparticle surface. The mechanical stiffness of the nanoengineered hydrogel can be tailored between 0.2 and 200 kPa simply by manipulating the size of the nanoparticles (4, 8, and 12 nm), as well as the concentrations of the nanoparticles and polymer. Moreover, cells can be easily encapsulated within the nanoparticulate-reinforced hydrogel network, showing high viability. In addition, encapsulated cells were able to sense and respond to matrix stiffness. Overall, these results demonstrate a facile approach to modulate the mechanical stiffness of collagen-based hydrogels and may have broad utility for various biomedical applications, including use as tissue-engineered scaffolds and cell/protein delivery vehicles. PMID:26670176
Simvastatin Ameliorates Matrix Stiffness-Mediated Endothelial Monolayer Disruption
Lampi, Marsha C.; Faber, Courtney J.; Huynh, John; Bordeleau, Francois; Zanotelli, Matthew R.; Reinhart-King, Cynthia A.
2016-01-01
Arterial stiffening accompanies both aging and atherosclerosis, and age-related stiffening of the arterial intima increases RhoA activity and cell contractility contributing to increased endothelium permeability. Notably, statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors whose pleiotropic effects include disrupting small GTPase activity; therefore, we hypothesized the statin simvastatin could be used to attenuate RhoA activity and inhibit the deleterious effects of increased age-related matrix stiffness on endothelial barrier function. Using polyacrylamide gels with stiffnesses of 2.5, 5, and 10 kPa to mimic the physiological stiffness of young and aged arteries, endothelial cells were grown to confluence and treated with simvastatin. Our data indicate that RhoA and phosphorylated myosin light chain activity increase with matrix stiffness but are attenuated when treated with the statin. Increases in cell contractility, cell-cell junction size, and indirect measurements of intercellular tension that increase with matrix stiffness, and are correlated with matrix stiffness-dependent increases in monolayer permeability, also decrease with statin treatment. Furthermore, we report that simvastatin increases activated Rac1 levels that contribute to endothelial barrier enhancing cytoskeletal reorganization. Simvastatin, which is prescribed clinically due to its ability to lower cholesterol, alters the endothelial cell response to increased matrix stiffness to restore endothelial monolayer barrier function, and therefore, presents a possible therapeutic intervention to prevent atherogenesis initiated by age-related arterial stiffening. PMID:26761203
Classical and numerical approaches to determining V-section band clamp axial stiffness
NASA Astrophysics Data System (ADS)
Barrans, Simon M.; Khodabakhshi, Goodarz; Muller, Matthias
2014-12-01
V-band clamp joints are used in a wide range of applications to connect circular flanges, for ducts, pipes and the turbocharger housing. Previous studies and research on V-bands are either purely empirical or analytical with limited applicability on the variety of V-band design and working conditions. In this paper models of the V-band are developed based on the classical theory of solid mechanics and the finite element method to study the behaviour of theV-bands under axial loading conditions. The good agreement between results from the developed FEA and the classical model support the suitability of the latter to modelV-band joints with diameters greater than 110mm under axial loading. The results from both models suggest that the axial stiffness for thisV-band cross section reaches a peak value for V-bands with radius of approximately 150 mmacross a wide range of coefficients of friction. Also, it is shown that the coefficient of friction and the wedge angle have a significant effect on the axial stiffness of V-bands.
Impact of blood pressure perturbations on arterial stiffness.
Lim, Jisok; Pearman, Miriam E; Park, Wonil; Alkatan, Mohammed; Machin, Daniel R; Tanaka, Hirofumi
2015-12-15
Although the associations between chronic levels of arterial stiffness and blood pressure (BP) have been fairly well studied, it is not clear whether and how much arterial stiffness is influenced by acute perturbations in BP. The primary aim of this study was to determine magnitudes of BP dependence of various measures of arterial stiffness during acute BP perturbation maneuvers. Fifty apparently healthy subjects, including 25 young (20-40 yr) and 25 older adults (60-80 yr), were studied. A variety of BP perturbations, including head-up tilt, head-down tilt, mental stress, isometric handgrip exercise, and cold pressor test, were used to encompass BP changes induced by physical, mental, and/or mechanical stimuli. When each index of arterial stiffness was plotted with mean BP, all arterial stiffness indices, including cardio-ankle vascular index or CAVI (r = 0.50), carotid-femoral pulse wave velocity or cfPWV (r = 0.51), brachial-ankle pulse wave velocity or baPWV (r = 0.61), arterial compliance (r = -0.42), elastic modulus (r = 0.52), arterial distensibility (r = -0.32), ?-stiffness index (r = 0.19), and Young's modulus (r = 0.35) were related to mean BP (all P < 0.01). Changes in CAVI, cfPWV, baPWV, and elastic modulus were significantly associated with changes in mean BP in the pooled conditions, while changes in arterial compliance, arterial distensibility, ?-stiffness index, and Young's modulus were not. In conclusion, this study demonstrated that BP changes in response to various forms of pressor stimuli were associated with the corresponding changes in arterial stiffness indices and that the strengths of associations with BP varied widely depending on what arterial stiffness indices were examined. PMID:26468262
NASA Technical Reports Server (NTRS)
Nolan, Steven Anthony
1987-01-01
A brief review of the annular seal theory as related to rotordynamics for liquid seals is presented. Also included is an overview of Childs and Kim's current theory for calculating empirical turbulence coefficients and predicting stiffness and damping coefficients for surface roughened damper seals. The designation sawtooth-pattern refers to a seal stator with a roughness pattern whose cross section normal to the seal axis resembles a sawtooth with the teeth directed against the flow. The net stiffness and damping coefficients for the eleven seals are compared to each other, a smooth seal, and the optimum-configuration damper seal previously tested. The experimental force coefficients, the net damping, and the net stiffness coefficients for four of the sawtooth seals are compared to the predictions of Childs and Kim's analysis. The sawtooth-pattern seal had less net damping than the hole-pattern seal but more than the smooth seal. The stiffness was comparable to the hole-pattern. Both the sawtooth and hole-pattern seals leaked less than the smooth seal, while the sawtooth-pattern seal with maximum damping leaked more than the hole-pattern seal. The theoretical predictions compared relatively poorly to the experimental results obtained for the rotordynamic coefficients of the seals investigation.
Local Rank Inference for Varying Coefficient Models.
Wang, Lan; Kai, Bo; Li, Runze
2009-12-01
By allowing the regression coefficients to change with certain covariates, the class of varying coefficient models offers a flexible approach to modeling nonlinearity and interactions between covariates. This paper proposes a novel estimation procedure for the varying coefficient models based on local ranks. The new procedure provides a highly efficient and robust alternative to the local linear least squares method, and can be conveniently implemented using existing R software package. Theoretical analysis and numerical simulations both reveal that the gain of the local rank estimator over the local linear least squares estimator, measured by the asymptotic mean squared error or the asymptotic mean integrated squared error, can be substantial. In the normal error case, the asymptotic relative efficiency for estimating both the coefficient functions and the derivative of the coefficient functions is above 96%; even in the worst case scenarios, the asymptotic relative efficiency has a lower bound 88.96% for estimating the coefficient functions, and a lower bound 89.91% for estimating their derivatives. The new estimator may achieve the nonparametric convergence rate even when the local linear least squares method fails due to infinite random error variance. We establish the large sample theory of the proposed procedure by utilizing results from generalized U-statistics, whose kernel function may depend on the sample size. We also extend a resampling approach, which perturbs the objective function repeatedly, to the generalized U-statistics setting; and demonstrate that it can accurately estimate the asymptotic covariance matrix. PMID:20657760
Parametric signal amplification to create a stiff optical bar
NASA Astrophysics Data System (ADS)
Somiya, K.; Kataoka, Y.; Kato, J.; Saito, N.; Yano, K.
2016-02-01
An optical cavity consisting of optically trapped mirrors makes a resonant bar that can be stiffer than diamond. A limitation of the stiffness arises in the length of the optical bar as a consequence of the finite light speed. High laser power and light mass mirrors are essential for realization of a long and stiff optical bar that can be useful for example in the gravitational-wave detector aiming at the observation of a signal from neutron-star collisions, supernovae, etc. In this letter, we introduce a parametric signal amplification scheme that realizes the long and stiff optical bar with a non-linear crystal inside the signal-recycling cavity.
Shah, Amy S.; Wadwa, R. Paul; Dabelea, Dana; Hamman, Richard F.; DAgostino, Ralph; Marcovina, Santica; Daniels, Stephen R.; Dolan, Lawrence M.; Fino, Nora F.; Urbina, Elaine M.
2016-01-01
Background Arterial stiffness is a useful parameter to predict future cardiovascular disease. Objective We sought to compare arterial stiffness in adolescents and young adults with and without type 1 diabetes (T1D) and explore the risk factors associated with the differences observed. Subjects and methods Carotid-femoral pulse wave velocity (PWV), augmentation index (AI75), and brachial distensibility (BrachD) were measured in 402 adolescents and young adults with T1D (age 18.8 3.3 yr, T1D duration 9.8 3.8 yr) and 206 non-diabetic controls that were frequency-matched by age, sex, and race/ethnicity in a cross-sectional study. General linear models were used to explore variables associated with an increase in arterial stiffness after adjustment for demographic and metabolic covariates. Results T1D status was associated with a higher PWV (5.9 0.05 vs. 5.7 0.1 m/s), AI75 (1.3 0.6 vs. ?1.9 0.7%), and lower BrachD (6.2 0.1 vs. 6.5 0.1%?/mmHg), all p < 0.05. In multivariate models, age, sex, race, adiposity, blood pressure, lipids, and the presence of microalbuminuria were found to be independent correlates of increased arterial stiffness. After adjustment for these risk factors, T1D status was still significantly associated with arterial stiffness (p < 0.05). Conclusions Peripheral and central subclinical vascular changes are present in adolescents and young adults with T1D compared to controls. Increased cardiovascular risk factors alone do not explain the observed differences in arterial stiffness among cases and controls. Identifying other risk factors associated with increased arterial stiffness in youth with T1D is critical to prevent future vascular complications. PMID:25912292
Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking
Shamaei, Kamran; Sawicki, Gregory S.; Dollar, Aaron M.
2013-01-01
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. PMID:23555839
Extracting Step Stiffness from Correlation Functions Consistent with the GWD
NASA Astrophysics Data System (ADS)
Benson, Amber; Richards, Howard
2003-03-01
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.
Dynamic Stiffness for Structures with Distributed Deterministic or Random Loads
NASA Astrophysics Data System (ADS)
LEUNG, A. Y. T.
2001-05-01
The dynamic stiffness method applies mainly to excitations of harmonic nodal forces. For distributed loads, modal analysis is generally required. In the case of a clamped-clamped beam, the modal decomposition of a uniformly distributed load by the eigenbeam functions inherits slow convergence because the finite loads at the beam-ends cannot be represented efficiently by the zero deflection and zero slope of the clamped-clamped beam functions. The computed reactions at the supports do not converge at all. The problem is eliminated in this paper by using the finite element interpolation functions for the distributed load. If the distributed load is adequately represented, explicit exact solutions are found. Otherwise, the residual load is expanded in the modal space. As the residual modal force is much smaller and agrees well with the clamped-clamped conditions, fast convergence is achieved. By means of the principle of superposition, a structure with members having distributed loads can be analyzed by two systems: one is associated with the individual members having distributed loads and the other is associated with resulting equivalent nodal forces. The required frequency functions are given for all possible cases. The results presented are exact if the load is interpolated adequately by finite element shape functions. Both deterministic and random loads are considered. Closed-form solutions are obtained for the first time.
NASA Astrophysics Data System (ADS)
Liu, Xingtian; Huang, Xiuchang; Hua, Hongxing
2013-07-01
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.
Stiff DAE integrator with sensitivity analysis capabilities
Energy Science and Technology Software Center (ESTSC)
2007-11-26
IDAS is a general purpose (serial and parallel) solver for differential equation (ODE) systems with senstivity analysis capabilities. It provides both forward and adjoint sensitivity analysis options.
NASA Technical Reports Server (NTRS)
Seale, Michael D.; Madaras, Eric I.
2000-01-01
The introduction of new, advanced composite materials into aviation systems requires it thorough understanding of the long-term effects of combined thermal and mechanical loading. As part of a study to evaluate the effects of thermal-mechanical cycling, it guided acoustic (Lamb) wave measurement system was used to measure the bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system uses a pulse/receive technique that excites an antisymmetric Lamb mode and measures the time-of-flight over a wide frequency range. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the velocity dispersion curve. A series of 16 and 32-ply composite laminates were subjected to it thermal-mechanical loading profile in load frames equipped with special environmental chambers. The composite systems studied were it graphite fiber reinforced amorphous thermoplastic polyimide and it graphite fiber reinforced bismaleimide thermoset. The samples were exposed to both high and low temperature extremes its well as high and low strain profiles. The bending and out-of-plane stiffnesses for composite sample that have undergone over 6,000 cycles of thermal-mechanical loading are reported. The Lamb wave generated elastic stiffness results have shown decreases of up to 20% at 4,936 loading cycles for the graphite/thermoplastic samples and up to 64% at 4,706 loading cycles for the graphite/thermoset samples.
NASA Technical Reports Server (NTRS)
Anderson, Roger A; Semonian, Joseph W
1954-01-01
A stability analysis is made of a long flat rectangular plate subjected to a uniform longitudinal compressive stress and supported along its longitudinal edges and along one or more longitudinal lines by elastic line supports. The elastic supports possess deflectional and rotational stiffness. Such configuration is an idealization of the compression cover skin and internal structure of a wing and tail surfaces. The results of the analysis are presented in the form of charts in which the buckling-stress coefficient is plotted against the buckle length of the plate for a wide range of support stiffnesses. The charts make possible the determination of the compressive buckling stress of plates supported by members whose stiffness may or may not be defined by elementary beam bending and twisting theory but yet whose effective restraint is amenable to evaluation. The deflectional and rotational stiffness provided by longitudinal stiffeners and full-depth webs is discussed and numerical examples are given to illustrate the application of the charts to the design of wing structures.
Second-order bounds for linear recurrences with negative coefficients
NASA Astrophysics Data System (ADS)
Berenhaut, Kenneth S.; Morton, Daniel C.
2006-02-01
This paper introduces a generalization of Fibonacci and Pell polynomials in order to obtain optimal second-order bounds for general linear recurrences with negative coefficients. An important aspect of the derived bounds is that they are applicable and easily computable. The results imply bounds on all entries in inverses of triangular matrices as well as on coefficients of reciprocals of power series.
Torque-stiffness-controlled dynamic walking with central pattern generators.
Huang, Yan; Vanderborght, Bram; Van Ham, Ronald; Wang, Qining
2014-12-01
Walking behavior is modulated by controlling joint torques in most existing passivity-based bipeds. Controlled Passive Walking with adaptable stiffness exhibits controllable natural motions and energy efficient gaits. In this paper, we propose torque-stiffness-controlled dynamic bipedal walking, which extends the concept of Controlled Passive Walking by introducing structured control parameters and a bio-inspired control method with central pattern generators. The proposed walking paradigm is beneficial in clarifying the respective effects of the external actuation and the internal natural dynamics. We present a seven-link biped model to validate the presented walking. Effects of joint torque and joint stiffness on gait selection, walking performance and walking pattern transitions are studied in simulations. The work in this paper develops a new solution of motion control of bipedal robots with adaptable stiffness and provides insights of efficient and sophisticated walking gaits of humans. PMID:25128320
Improved Equivalent Linearization Implementations Using Nonlinear Stiffness Evaluation
NASA Technical Reports Server (NTRS)
Rizzi, Stephen A.; Muravyov, Alexander A.
2001-01-01
This report documents two new implementations of equivalent linearization for solving geometrically nonlinear random vibration problems of complicated structures. The implementations are given the acronym ELSTEP, for "Equivalent Linearization using a STiffness Evaluation Procedure." Both implementations of ELSTEP are fundamentally the same in that they use a novel nonlinear stiffness evaluation procedure to numerically compute otherwise inaccessible nonlinear stiffness terms from commercial finite element programs. The commercial finite element program MSC/NASTRAN (NASTRAN) was chosen as the core of ELSTEP. The FORTRAN implementation calculates the nonlinear stiffness terms and performs the equivalent linearization analysis outside of NASTRAN. The Direct Matrix Abstraction Program (DMAP) implementation performs these operations within NASTRAN. Both provide nearly identical results. Within each implementation, two error minimization approaches for the equivalent linearization procedure are available - force and strain energy error minimization. Sample results for a simply supported rectangular plate are included to illustrate the analysis procedure.
Operator-Based Preconditioning of Stiff Hyperbolic Systems
Reynolds, Daniel R.; Samtaney, Ravi; Woodward, Carol S.
2009-02-09
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.
The measurement of plain weft-knitted fabric stiffness
NASA Astrophysics Data System (ADS)
Haji Mohamad, Ayhan; Cassidy, Thomas; Brydon, Alan; Halley, Dave
2012-05-01
A new instrument and a test method are presented in this paper that can evaluate the stiffness of plain weft-knitted fabrics. The WIRA Instrumentation Tester can measure torsion data for various flexible fibre assemblies whilst they are being twisted. The torsional properties of two types of fabrics, namely nonwoven and knitted fabrics, were analyzed. Then, comparisons between bending rigidity and torsional rigidity have been conducted using FAST-2, Shirley, Heart Loop and the new WIRA method for the assessment of fabric stiffness. The results show high correlation between bending rigidity and torsional rigidity in assessment of nonwoven fabric stiffness; they also reveal that the WIRA tester and torsional rigidity are more suitable for characterizing the stiffness of plain weft-knitted fabrics than the other test methods.
Extreme stiffness tunability through the excitation of nonlinear defect modes
NASA Astrophysics Data System (ADS)
Serra-Garcia, M.; Lydon, J.; Daraio, C.
2016-01-01
The incremental stiffness characterizes the variation of a material's force response to a small deformation change. In lattices with noninteracting vibrational modes, the excitation of localized states does not have any effect on material properties, such as the incremental stiffness. We report that, in nonlinear lattices, driving a defect mode introduces changes in the static force-displacement relation of the material. By varying the defect excitation frequency and amplitude, the incremental stiffness can be tuned continuously to arbitrarily large positive or negative values. Furthermore, the defect excitation parameters also determine the displacement region at which the force-displacement relation is being tuned. We demonstrate this phenomenon experimentally in a compressed array of spheres tuning its incremental stiffness from a finite positive value to zero and continuously down to negative infinity.
Stiffness Corrections for the Vibration Frequency of a Stretched Wire
ERIC Educational Resources Information Center
Hornung, H. G.; Durie, M. J.
1977-01-01
Discusses the need of introducing corrections due to wire stiffness arising from end constraints and wire axis distribution curvature in the measurement of ac electrical frequency by exciting transverse standing waves in a stretched steel wire. (SL)
Stiffness of Carpentry Connections - Numerical Modelling vs. Experimental Test
NASA Astrophysics Data System (ADS)
Kekeliak, Milo; Gocl, Jozef; Vi?an, Josef
2015-12-01
In this paper, numerical modelling of the traditional carpentry connection with mortise and tenon is presented. Numerical modelling is focused on its stiffness and the results are compared to results of experimental tests carried out by (Feio, 2005) [6]. To consider soft behaviour of wood in carpentry connections, which are related to its surface roughness and geometrical accuracy of the contact surfaces, the characteristics of the normal contact stiffness, determined experimentally, are introduced in the numerical model. Parametric study by means of numerical modelling with regard to the sensitivity of connection stiffness to contact stiffness is presented. Based on the study results, in conclusion there are presented relevant differences between the results of numerical modelling and experimental tests (Feio, 2005) [6].
Study of flexural stiffness in delaminated composite plates
NASA Astrophysics Data System (ADS)
Kwon, Y. W.; Weiseman, K.
This paper studied the effect of delamination on the flexural stiffness of laminated composite plates using the FEM. A plate bending element, which has displacements as degrees of freedom at nodes but not rotations, was used. The plate bending element includes the transverse shear deformation. Both angle-ply (+/- theta deg) and cross-ply (0/90 deg) laminates were considered with delamination between the two layers. The reduction in flexural stiffness was calculated by comparing deflections.
Gear mesh stiffness and load sharing in planetary gearing
NASA Technical Reports Server (NTRS)
Kasuba, R.; August, R.
1984-01-01
An interactive computerized analysis was developed for determining load sharing among planetary gears. The load sharing is established as a function of transmitted torque, degree of sun gear fixity, component flexibility, gear tooth quality, and phasing of individual planet gears. A nonlinear variable gear tooth mesh stiffness model was used to simulate the sun/plant and planet/ring gear meshes. The determined load sharing and gear mesh stiffness parameters then can be used for the subsequent assessment of dynamic load factors.
Pediatric stiff-person syndrome with renal failure
Kumar, M. Veerendra; Savida, P.
2016-01-01
Stiff-person syndrome (SPS) is an autoimmune neuronitis with progressive myoclonus and stiffness. It is a rare but treatable disorder with few case reports in children. SPS is due to autoantibodies against the enzyme glutamic acid decarboxylase which is present in neuronal and nonneuronal tissues. This is the case report of an 8-year-old boy with clinical and investigational features suggestive of SPS with associated myoglobin-induced renal failure, who completely recovered with treatment.
Effects of age and diabetes on scleral stiffness.
Coudrillier, Baptiste; Pijanka, Jacek; Jefferys, Joan; Sorensen, Thomas; Quigley, Harry A; Boote, Craig; Nguyen, Thao D
2015-07-01
The effects of diabetes on the collagen structure and material properties of the sclera are unknown but may be important to elucidate whether diabetes is a risk factor for major ocular diseases such as glaucoma. This study provides a quantitative assessment of the changes in scleral stiffness and collagen fiber alignment associated with diabetes. Posterior scleral shells from five diabetic donors and seven non-diabetic donors were pressurized to 30?mm Hg. Three-dimensional surface displacements were calculated during inflation testing using digital image correlation (DIC). After testing, each specimen was subjected to wide-angle X-ray scattering (WAXS) measurements of its collagen organization. Specimen-specific finite element models of the posterior scleras were generated from the experimentally measured geometry. An inverse finite element analysis was developed to determine the material properties of the specimens, i.e., matrix and fiber stiffness, by matching DIC-measured and finite element predicted displacement fields. Effects of age and diabetes on the degree of fiber alignment, matrix and collagen fiber stiffness, and mechanical anisotropy were estimated using mixed effects models accounting for spatial autocorrelation. Older age was associated with a lower degree of fiber alignment and larger matrix stiffness for both diabetic and non-diabetic scleras. However, the age-related increase in matrix stiffness was 87% larger in diabetic specimens compared to non-diabetic controls and diabetic scleras had a significantly larger matrix stiffness (p?=?0.01). Older age was associated with a nearly significant increase in collagen fiber stiffness for diabetic specimens only (p?=?0.06), as well as a decrease in mechanical anisotropy for non-diabetic scleras only (p?=?0.04). The interaction between age and diabetes was not significant for all outcomes. This study suggests that the age-related increase in scleral stiffness is accelerated in eyes with diabetes, which may have important implications in glaucoma. PMID:25751456
Influence of Compression and Stiffness Apparel on Vertical Jump Performance.
Wannop, John W; Worobets, Jay T; Madden, Ryan; Stefanyshyn, Darren J
2016-04-01
Wannop, JW, Worobets, JT, Madden, R, and Stefanyshyn, DJ. Influence of compression and stiffness apparel on vertical jump performance. J Strength Cond Res 30(4): 1093-1101, 2016-Compression apparel alters both compression of the soft tissues and the hip joint stiffness of athletes. It is not known whether it is the compression elements, the stiffness elements, or some combination that increases performance. Therefore, the purpose of this study was to determine how systematically increasing upper leg compression and hip joint stiffness independently from one another affects vertical jumping performance. Ten male athletes performed countermovement vertical jumps in 8 concept apparel conditions and 1 control condition (loose fitting shorts). The 8 apparel conditions, 4 that specifically altered the amount of compression exerted on the thigh and 4 that altered the hip joint stiffness by means of elastic thermoplastic polyurethane bands, were tested on 2 separate testing sessions (one testing the compression apparel and the other testing the stiffness apparel). Maximum jump height was measured, while kinematic data of the hip, knee, and ankle joint were recorded with a high-speed camera (480 Hz). Both compression and stiffness apparel can have a positive influence on vertical jumping performance. The increase in jump height for the optimal compression was due to increased hip joint range of motion and a trend of increasing the jump time. Optimal stiffness also increased jump height and had the trend of decreasing the hip joint range of motion and hip joint angular velocity. The exact mechanisms by which apparel interventions alter performance is not clear, but it may be due to alterations to the force-length and force-velocity relationships of muscle. PMID:27003453
The initial torsional stiffness of shells with interior webs
NASA Technical Reports Server (NTRS)
Kuhn, Paul
1935-01-01
A method of calculating the stresses and torsional stiffness of thin shells with interior webs is summarized. Comparisons between experimental and calculated results are given for 3 duralumin beams, 5 stainless steel beams and 2 duralumin wings. It is concluded that if the theoretical stiffness is multiplied by a correction factor of 0.9, experimental values may be expected to check calculated values within about 10 percent.
Modeling, Modal Properties, and Mesh Stiffness Variation Instabilities of Planetary Gears
NASA Technical Reports Server (NTRS)
Parker, Robert G.; Lin, Jian; Krantz, Timothy L. (Technical Monitor)
2001-01-01
Planetary gear noise and vibration are primary concerns in their applications in helicopters, automobiles, aircraft engines, heavy machinery and marine vehicles. Dynamic analysis is essential to the noise and vibration reduction. This work analytically investigates some critical issues and advances the understanding of planetary gear dynamics. A lumped-parameter model is built for the dynamic analysis of general planetary gears. The unique properties of the natural frequency spectra and vibration modes are rigorously characterized. These special structures apply for general planetary gears with cyclic symmetry and, in practically important case, systems with diametrically opposed planets. The special vibration properties are useful for subsequent research. Taking advantage of the derived modal properties, the natural frequency and vibration mode sensitivities to design parameters are investigated. The key parameters include mesh stiffnesses, support/bearing stiffnesses, component masses, moments of inertia, and operating speed. The eigen-sensitivities are expressed in simple, closed-form formulae associated with modal strain and kinetic energies. As disorders (e.g., mesh stiffness variation. manufacturing and assembling errors) disturb the cyclic symmetry of planetary gears, their effects on the free vibration properties are quantitatively examined. Well-defined veering rules are derived to identify dramatic changes of natural frequencies and vibration modes under parameter variations. The knowledge of free vibration properties, eigen-sensitivities, and veering rules provide important information to effectively tune the natural frequencies and optimize structural design to minimize noise and vibration. Parametric instabilities excited by mesh stiffness variations are analytically studied for multi-mesh gear systems. The discrepancies of previous studies on parametric instability of two-stage gear chains are clarified using perturbation and numerical methods. The operating conditions causing parametric instabilities are expressed in closed-form suitable for design guidance. Using the well-defined modal properties of planetary gears, the effects of mesh parameters on parametric instability are analytically identified. Simple formulae are obtained to suppress particular instabilities by adjusting contact ratios and mesh phasing.
Mller, Jan; Wilms, Michael; Oberhoffer, Renate
2015-05-01
Measures of arterial stiffness are indicators for cardiovascular health and predictors of cardiovascular events. Arterial stiffness is responsive to acute physiologic stressors such as exercise. However, the acute effects of intensive exercise and recovery on arterial stiffness are controversial. Thirty-seven healthy middle- and long-distance runners (33 men, mean age 26.56.6years) underwent evaluation of their cardiovascular stiffness at rest, after a 15-minute warm-up, immediately after vigorous running 3km at the pace of their 10-km personal best, and finally 30minutes after terminating their workout. Peripheral and central systolic blood pressure, as well as augmentation index and pulse wave velocity (PWV), increased during exercise in comparison to baseline (P<.001, general linear model). Thirty minutes after terminating the workout, a drop in peripheral blood pressure (P<.001), central blood pressure (P<.001), and PWV (P=.001) below baseline was observed. Therefore, the authors found that exercise of either moderate or vigorous intensity causes a temporary increase in arterial stiffness in middle- and long-distance runners. PMID:25782686
TA, Sandhya
2014-01-01
Introduction: Arterial compliance will result in stabilizing the fluctuations in arterial pressure and blood flow. So arterial stiffness can be a good indicator for monitoring the cardiovascular system. Arterial stiffness can be measured using indices like reflection index (RI), stiffness index (SI) and Brachial Finger Pulse Wave Velocity (BFPWV). Objectives: Aim of our study was to evaluate the changes in RI, SI and BFPWV during different phases of the menstrual cycle and to correlate RI with SI in healthy female subjects between the age group of 18-30 years from Bangalore, India. Materials and Methods: Basal recordings of RI and SI were determined by Photo Pulse Plethysmography (PPG) picked up from the fingertip using BIOPAC system and BFPWV was obtained using Doppler. Recordings were obtained at three different time points during the menstrual cycle. Analysis was done using repeated measures ANOVA with Bonferroni correction. Result: There was a significant decrease in above parameters p <0.05 during the mid-cycle. Correlation between RI and SI was also significant p<0.05. Conclusion: These findings suggests that the menstrual cycle affects the arterial stiffness and one of the factor is oestrogen. Hence, women are less prone to the incidence of cardiovascular diseases before menopause. Screening for arterial stiffness in a general population, using these indices is valid, economical and reliable. PMID:25386420
Therapeutic modification of arterial stiffness: An update and comprehensive review.
Wu, Ching-Fen; Liu, Pang-Yen; Wu, Tsung-Jui; Hung, Yuan; Yang, Shih-Ping; Lin, Gen-Min
2015-11-26
Arterial stiffness has been recognized as a marker of cardiovascular disease and associated with long-term worse clinical outcomes in several populations. Age, hypertension, smoking, and dyslipidemia, known as traditional vascular risk factors, as well as diabetes, obesity, and systemic inflammation lead to both atherosclerosis and arterial stiffness. Targeting multiple modifiable risk factors has become the main therapeutic strategy to improve arterial stiffness in patients at high cardiovascular risk. Additionally to life style modifications, long-term ?-3 fatty acids (fish oil) supplementation in diet may improve arterial stiffness in the population with hypertension or metabolic syndrome. Pharmacological treatment such as renin-angiotensin-aldosterone system antagonists, metformin, and 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors were useful in individuals with hypertension and diabetes. In obese population with obstructive sleep apnea, weight reduction, aerobic exercise, and continuous positive airway pressure treatment may also improve arterial stiffness. In the populations with chronic inflammatory disease such as rheumatoid arthritis, a use of antibodies against tumor necrosis factor-alpha could work effectively. Other therapeutic options such as renal sympathetic nerve denervation for patients with resistant hypertension are investigated in many ongoing clinical trials. Therefore our comprehensive review provides knowledge in detail regarding many aspects of pathogenesis, measurement, and management of arterial stiffness in several populations, which would be helpful for physicians to make clinical decision. PMID:26635922
Changes in human knee ligament stiffness secondary to osteoarthritis.
Fishkin, Zair; Miller, David; Ritter, Christopher; Ziv, Israel
2002-03-01
Stiffness of the medial (MCL) and lateral (LCL) collateral ligaments was compared between a group of 10 patients undergoing total knee arthroplasty for varus degenerative osteoarthritis (OAP), a group of 10 osteoarthritic cadaveric knees (OAC), and a group of 10 non-osteoarthritic cadaveric knees (NOA). A load-elongation curve was obtained for the medial and lateral compartments of each knee using an instrumented Moreland spreader. A strain gage (SG) was attached to the spreader handle and strain was calibrated to load applied against the spread distance. In extension, medial compartment stiffness of the OAP, OAC, and NOA groups was 60.7+/-16, 52.8+/-9.3 and 21.4+/-5.0 N/mm, respectively. Lateral compartment stiffness in extension was 29.2+/-9.2, 33.3+/-10.3 and 19.5+/-5.3 N/mm, for OAP, OAC, and NOA, respectively. Differences in stiffness between the OAP and OAC groups were not statistically significant (p > 0.05). However, the osteoarthritic groups (OAP and OAC) demonstrated a statistically significantly (p < 0.05) increase in ligament stiffness when compared to the NOA group. Following knee arthroplasty, stiffer medial structures in extension may lead to flexion contracture and accelerated polyethylene wear. Adequate bone resection, in conjunction with soft tissue release may alleviate the threefold increase in stiffness observed in the medial compartment secondary to OA without jeopardizing joint stability. PMID:11918298
Mesenchymal Stem Cell Durotaxis Depends on Substrate Stiffness Gradient Strength
Vincent, Ludovic G.; Choi, Yu Suk; Alonso-Latorre, Baldomero; del Álamo, Juan C.; Engler, Adam J.
2013-01-01
Mesenchymal stem cells (MSCs) respond to niche elasticity, which varies between and within tissues. Stiffness gradients result from pathological conditions but also occur through normal variation, e.g. muscle. MSCs undergo directed migration even in response to shallow stiffness gradients before differentiating. More refined gradients of both stiffness range and strength are needed to better understand mechanical regulation of migration in normal and disease pathologies. We describe polyacrylamide stiffness gradient fabrication using three distinct systems that generate stiffness gradients of physiological (1 Pa/µm), pathological (10 Pa/µm), and step (≥ 100Pa/um) strength spanning physiologically relevant stiffness for most soft tissue, i.e. 1–12 kPa. MSCs migrated to the stiffest region for each gradient. Time-lapse microscopy revealed that migration velocity scaled directly with gradient strength. Directed migration was reduced in the presence of the contractile agonist lysophosphatidic acid (LPA) and cytoskeletal-perturbing drugs nocodazole and cytochalasin; LPA- and nocodazole-treated cells remained spread and protrusive, while cytochalasin-treated cells did not. Untreated and nocodazole-treated cells spread in a similar manner, but nocodazole-treated cells had greatly diminished traction forces. These data suggest that actin is required for migration whereas microtubules are required for directed migration. The data also imply that in vivo, MSCs may have a more significant contribution to repairs in stiffer regions where they may preferentially accumulate. PMID:23390141
Therapeutic modification of arterial stiffness: An update and comprehensive review
Wu, Ching-Fen; Liu, Pang-Yen; Wu, Tsung-Jui; Hung, Yuan; Yang, Shih-Ping; Lin, Gen-Min
2015-01-01
Arterial stiffness has been recognized as a marker of cardiovascular disease and associated with long-term worse clinical outcomes in several populations. Age, hypertension, smoking, and dyslipidemia, known as traditional vascular risk factors, as well as diabetes, obesity, and systemic inflammation lead to both atherosclerosis and arterial stiffness. Targeting multiple modifiable risk factors has become the main therapeutic strategy to improve arterial stiffness in patients at high cardiovascular risk. Additionally to life style modifications, long-term ω-3 fatty acids (fish oil) supplementation in diet may improve arterial stiffness in the population with hypertension or metabolic syndrome. Pharmacological treatment such as renin-angiotensin-aldosterone system antagonists, metformin, and 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors were useful in individuals with hypertension and diabetes. In obese population with obstructive sleep apnea, weight reduction, aerobic exercise, and continuous positive airway pressure treatment may also improve arterial stiffness. In the populations with chronic inflammatory disease such as rheumatoid arthritis, a use of antibodies against tumor necrosis factor-alpha could work effectively. Other therapeutic options such as renal sympathetic nerve denervation for patients with resistant hypertension are investigated in many ongoing clinical trials. Therefore our comprehensive review provides knowledge in detail regarding many aspects of pathogenesis, measurement, and management of arterial stiffness in several populations, which would be helpful for physicians to make clinical decision. PMID:26635922
Non-crossbridge stiffness in active muscle fibres.
Colombini, Barbara; Nocella, Marta; Bagni, Maria Angela
2016-01-01
Stretching of an activated skeletal muscle induces a transient tension increase followed by a period during which the tension remains elevated well above the isometric level at an almost constant value. This excess of tension in response to stretching has been called 'static tension' and attributed to an increase in fibre stiffness above the resting value, named 'static stiffness'. This observation was originally made, by our group, in frog intact muscle fibres and has been confirmed more recently, by us, in mammalian intact fibres. Following stimulation, fibre stiffness starts to increase during the latent period well before crossbridge force generation and it is present throughout the whole contraction in both single twitches and tetani. Static stiffness is dependent on sarcomere length in a different way from crossbridge force and is independent of stretching amplitude and velocity. Static stiffness follows a time course which is distinct from that of active force and very similar to the myoplasmic calcium concentration time course. We therefore hypothesize that static stiffness is due to a calcium-dependent stiffening of a non-crossbridge sarcomere structure, such as the titin filament. According to this hypothesis, titin, in addition to its well-recognized role in determining the muscle passive tension, could have a role during muscle activity. PMID:26792325
Lekesiz, Huseyin; Katsube, Noriko; Rokhlin, Stanislav I.; Seghi, Robert R.
2011-01-01
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
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
Hole spin relaxation and coefficients in Landau-Lifshitz-Gilbert equation in ferromagnetic (Ga,Mn)As
NASA Astrophysics Data System (ADS)
Shen, K.; Wu, M. W.
2012-02-01
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.
Levy, Daniel; Larson, Martin G; Benjamin, Emelia J; Newton-Cheh, Christopher; Wang, Thomas J; Hwang, Shih-Jen; Vasan, Ramachandran S; Mitchell, Gary F
2007-01-01
Background About one quarter of adults are hypertensive and high blood pressure carries increased risk for heart disease, stroke, kidney disease and death. Increased arterial stiffness is a key factor in the pathogenesis of systolic hypertension and cardiovascular disease. Substantial heritability of blood-pressure (BP) and arterial-stiffness suggests important genetic contributions. Methods In Framingham Heart Study families, we analyzed genome-wide SNP (Affymetrix 100K GeneChip) associations with systolic (SBP) and diastolic (DBP) BP at a single examination in 19711975 (n = 1260), at a recent examination in 19982001 (n = 1233), and long-term averaged SBP and DBP from 19712001 (n = 1327, mean age 52 years, 54% women) and with arterial stiffness measured by arterial tonometry (carotid-femoral and carotid-brachial pulse wave velocity, forward and reflected pressure wave amplitude, and mean arterial pressure; 19982001, n = 644). In primary analyses we used generalized estimating equations in models for an additive genetic effect to test associations between SNPs and phenotypes of interest using multivariable-adjusted residuals. A total of 70,987 autosomal SNPs with minor allele frequency ? 0.10, genotype call rate ? 0.80, and Hardy-Weinberg equilibrium p ? 0.001 were analyzed. We also tested for association of 69 SNPs in six renin-angiotensin-aldosterone pathway genes with BP and arterial stiffness phenotypes as part of a candidate gene search. Results In the primary analyses, none of the associations attained genome-wide significance. For the six BP phenotypes, seven SNPs yielded p values < 10-5. The lowest p-values for SBP and DBP respectively were rs10493340 (p = 1.7 10-6) and rs1963982 (p = 3.3 10-6). For the five tonometry phenotypes, five SNPs had p values < 10-5; lowest p-values were for reflected wave (rs6063312, p = 2.1 10-6) and carotid-brachial pulse wave velocity (rs770189, p = 2.5 10-6) in MEF2C, a regulator of cardiac morphogenesis. We found only weak association of SNPs in the renin-angiotensin-aldosterone pathway with BP or arterial stiffness. Conclusion These results of genome-wide association testing for blood pressure and arterial stiffness phenotypes in an unselected community-based sample of adults may aid in the identification of the genetic basis of hypertension and arterial disease, help identify high risk individuals, and guide novel therapies for hypertension. Additional studies are needed to replicate any associations identified in these analyses. PMID:17903302
Coefficients of associated Legendre functions
NASA Technical Reports Server (NTRS)
Peasley, Q. D.
1976-01-01
The exact coefficients for the explicit forms of the associated Legendre functions Pm for integer values of m,n=0,1,2,...25 are presented in tabular form together with two cross-referenced listings of the zeroes for these functions rounded to five decimal places. The unfactored coefficients and the interger coefficients are presented in adjacent columns for each function. The greatest common factor and divisor have been removed and listed separately for the integer coefficients.
Stiffness threshold of randomly distributed carbon nanotube networks
NASA Astrophysics Data System (ADS)
Chen, Yuli; Pan, Fei; Guo, Zaoyang; Liu, Bin; Zhang, Jianyu
2015-11-01
For carbon nanotube (CNT) networks, with increasing network density, there may be sudden changes in the properties, such as the sudden change in electrical conductivity at the electrical percolation threshold. In this paper, the change in stiffness of the CNT networks is studied and especially the existence of stiffness threshold is revealed. Two critical network densities are found to divide the stiffness behavior into three stages: zero stiffness, bending dominated and stretching dominated stages. The first critical network density is a criterion to judge whether or not the network is capable of carrying load, defined as the stiffness threshold. The second critical network density is a criterion to measure whether or not most of the CNTs in network are utilized effectively to carry load, defined as bending-stretching transitional threshold. Based on the geometric probability analysis, a theoretical methodology is set up to predict the two thresholds and explain their underlying mechanisms. The stiffness threshold is revealed to be determined by the statical determinacy of CNTs in the network, and can be estimated quantitatively by the stabilization fraction of network, a newly proposed parameter in this paper. The other threshold, bending-stretching transitional threshold, which signs the conversion of dominant deformation mode, is verified to be well evaluated by the proposed defect fraction of network. According to the theoretical analysis as well as the numerical simulation, the average intersection number on each CNT is revealed as the only dominant factor for the electrical percolation and the stiffness thresholds, it is approximately 3.7 for electrical percolation threshold, and 5.2 for the stiffness threshold of 2D networks. For 3D networks, they are 1.4 and 4.4. And it also affects the bending-stretching transitional threshold, together with the CNT aspect ratio. The average intersection number divided by the fourth root of CNT aspect ratio is found to be an invariant at the bending-stretching transitional threshold, which is 6.7 and 6.3 for 2D and 3D networks, respectively. Based on this study, a simple piecewise expression is summarized to describe the relative stiffness of CNT networks, in which the relative stiffness of networks depends on the relative network density as well as the CNT aspect ratio. This formula provides a solid theoretical foundation for the design optimization and property prediction of CNT networks.
Gender Differences in Leg Stiffness and Stiffness Recruitment Strategy During Two-Legged Hopping
Padua, Darin A.; Arnold, Brent L.; Carcia, Christopher R.; Granata, Kevin P.
2006-01-01
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. PMID:15730945
Bia, Daniel; Galli, Cintia; Valtuille, Rodolfo; Zócalo, Yanina; Wray, Sandra A; Armentano, Ricardo L; Cabrera Fischer, Edmundo I
2015-01-01
Background. Adequate fluid management could be essential to minimize high arterial stiffness observed in chronically hemodialyzed patients (CHP). Aim. To determine the association between body fluid status and central and peripheral arterial stiffness levels. Methods. Arterial stiffness was assessed in 65 CHP by measuring the pulse wave velocity (PWV) in a central arterial pathway (carotid-femoral) and in a peripheral pathway (carotid-brachial). A blood pressure-independent regional arterial stiffness index was calculated using PWV. Volume status was assessed by whole-body multiple-frequency bioimpedance. Patients were first observed as an entire group and then divided into three different fluid status-related groups: normal, overhydration, and dehydration groups. Results. Only carotid-femoral stiffness was positively associated (P < 0.05) with the hydration status evaluated through extracellular/intracellular fluid, extracellular/Total Body Fluid, and absolute and relative overhydration. Conclusion. Volume status and overload are associated with central, but not peripheral, arterial stiffness levels with independence of the blood pressure level, in CHP. PMID:26167301
Bia, Daniel; Galli, Cintia; Valtuille, Rodolfo; Zócalo, Yanina; Wray, Sandra A.; Armentano, Ricardo L.; Cabrera Fischer, Edmundo I.
2015-01-01
Background. Adequate fluid management could be essential to minimize high arterial stiffness observed in chronically hemodialyzed patients (CHP). Aim. To determine the association between body fluid status and central and peripheral arterial stiffness levels. Methods. Arterial stiffness was assessed in 65 CHP by measuring the pulse wave velocity (PWV) in a central arterial pathway (carotid-femoral) and in a peripheral pathway (carotid-brachial). A blood pressure-independent regional arterial stiffness index was calculated using PWV. Volume status was assessed by whole-body multiple-frequency bioimpedance. Patients were first observed as an entire group and then divided into three different fluid status-related groups: normal, overhydration, and dehydration groups. Results. Only carotid-femoral stiffness was positively associated (P < 0.05) with the hydration status evaluated through extracellular/intracellular fluid, extracellular/Total Body Fluid, and absolute and relative overhydration. Conclusion. Volume status and overload are associated with central, but not peripheral, arterial stiffness levels with independence of the blood pressure level, in CHP. PMID:26167301
Rotational Raman lidar for obtaining aerosol scattering coefficients.
Kim, Dukhyeon; Cha, Hyungki
2005-07-01
Two-channel lidar signals that are composed of total rotational scattering and elastic signals provide good information about aerosol scattering coefficients. We can calculate the aerosol backscattering coefficient and extinction coefficient directly, without making any assumption or calibration. Generally, a high-spectral-resolution lidar is used for aerosol monitoring, but we have designed a new low-spectral-resolution lidar system that contains both kinds of scattering information simultaneously, and we have retrieved the aerosol scattering coefficient. The results show that there is no need to assume any relation between aerosol backscattering and extinction or to consider any wavelength calibration to determine the aerosol scattering coefficient. PMID:16075552
The equilibrium state method for hyperbolic conservation laws with stiff reaction terms
NASA Astrophysics Data System (ADS)
Zhang, Bin; Liu, Hong; Chen, Fang; Wang, Jian Hang
2014-04-01
A new fractional-step method is proposed for numerical simulations of hyperbolic conservation laws with stiff source terms arising from chemically reactive flows. In stiff reaction problems, a well-known spurious numerical phenomenon, the incorrect propagation speed of discontinuities, may occur in general fractional-step algorithm due to the underresolved numerical solution in both space and time. The basic idea of the present proposed scheme is to replace the cell average representation with a two-equilibrium states reconstruction during the reaction step, which allows us to obtain the correct propagation of discontinuities for stiff reaction problems in an underresolved mesh. Because the definition of these two-equilibrium states for each transition cell is independent of its neighboring cells, the proposed method can be extended to multi-dimensional problems directly. In addition, this method is promising to deal with more complicated real-world problems after being extended to multi-species/multi-reactions system. Extensive numerical examples for one- and two-dimensional scalar and Euler system demonstrate the reliability and robustness of this novel method.
Redox regulation of morphology, cell stiffness, and lectin-induced aggregation of human platelets.
Shamova, Ekaterina V; Gorudko, Irina V; Drozd, Elizaveta S; Chizhik, Sergey A; Martinovich, Grigory G; Cherenkevich, Sergey N; Timoshenko, Alexander V
2011-02-01
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 6mM) 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
Explicit Integration of Extremely Stiff Reaction Networks: Quasi-Steady-State Methods
Guidry, Mike W; Harris, James A
2013-01-01
A preceding paper [1] 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, even for extremely stiff networks, and in many cases give somewhat better integration speed than for asymptotic methods. As for asymptotic methods, we will find that QSS methods give correct results, but with non-competitive integration speed as equilibrium is approached. Thus, we shall find that both asymptotic and QSS methods must be supplemented with partial equilibrium methods as equilibrium is approached to remain competitive with implicit methods.
Electron temperature critical gradient and transport stiffness in DIII-D
NASA Astrophysics Data System (ADS)
Smith, S. P.; Petty, C. C.; White, A. E.; Holland, C.; Bravenec, R.; Austin, M. E.; Zeng, L.; Meneghini, O.
2015-08-01
In a continuing effort to validate turbulent transport models, the electron energy flux has been probed as a function of electron temperature gradient on the DIII-D tokamak. In the scan of gradient, a critical electron temperature gradient has been found in the electron heat fluxes and stiffness at various radii in L-mode plasmas. The TGLF reduced turbulent transport model (Staebler et al 2007 Phys. Plasmas 14 055909) and full gyrokinetic GYRO model (Candy and Waltz 2003 J. Comput. Phys. 186 545) recover the general trend of increasing electron energy flux with increasing electron temperature gradient scale length, but they do not predict the absolute level of transport at all radii and gradients. Comparing the experimental observations of incremental (heat pulse) diffusivity and stiffness to the models’ reveals that TGLF reproduces the trends in increasing diffusivity and stiffness with increasing electron temperature gradient scale length with a critical gradient behavior. The critical gradient of TGLF is found to have a dependence on q95, contrary to the independence of the experimental critical gradient from q95.
Hughson, Richard L; Robertson, Andrew D; Arbeille, Philippe; Shoemaker, J Kevin; Rush, James W E; Fraser, Katelyn S; Greaves, Danielle K
2016-03-01
Removal of the normal head-to-foot gravity vector and chronic weightlessness during spaceflight might induce cardiovascular and metabolic adaptations related to changes in arterial pressure and reduction in physical activity. We tested hypotheses that stiffness of arteries located above the heart would be increased postflight, and that blood biomarkers inflight would be consistent with changes in vascular function. Possible sex differences in responses were explored in four male and four female astronauts who lived on the International Space Station for 6 mo. Carotid artery distensibility coefficient (P = 0.005) and β-stiffness index (P = 0.006) reflected 17-30% increases in arterial stiffness when measured within 38 h of return to Earth compared with preflight. Spaceflight-by-sex interaction effects were found with greater changes in β-stiffness index in women (P = 0.017), but greater changes in pulse wave transit time in men (P = 0.006). Several blood biomarkers were changed from preflight to inflight, including an increase in an index of insulin resistance (P < 0.001) with a spaceflight-by-sex term suggesting greater change in men (P = 0.034). Spaceflight-by-sex interactions for renin (P = 0.016) and aldosterone (P = 0.010) indicated greater increases in women than men. Six-month spaceflight caused increased arterial stiffness. Altered hydrostatic arterial pressure gradients as well as changes in insulin resistance and other biomarkers might have contributed to alterations in arterial properties, including sex differences between male and female astronauts. PMID:26747504
A LONGITUDINAL PERSPECTIVE ON THE CONUNDRUM OF CENTRAL ARTERIAL STIFFNESS, BLOOD PRESSURE AND AGING
Scuteri, Angelo; Morrell, Christopher H.; Orru, Marco; Strait, James B.; Tarasov, Kirill V.; AlGhatrif, Majd; Pina Ferreli, Liana Anna; Loi, Francesco; Pilia, Maria Grazia; Delitala, Alessandro; Spurgeon, Harold; Najjar, Samer S.; Lakatta, Edward G.
2014-01-01
The age-associated increase in arterial stiffness has long been considered to parallel or to cause the age-associated increase in blood pressure (BP). Yet, the rates at which pulse wave velocity (PWV), a measure of arterial stiffness, and BP trajectories change over time within individuals who differ by age and sex have not been assessed and compared. This study determined the evolution of BP and aortic PWV trajectories over a 9.4-year follow-up in over 4,000 community dwelling men and women of 20100 years of age at entry into the SardiNIA Study. Linear mixed effects model analyses revealed that PWV accelerates with time over the observation period, at about the same rate over the entire age range in both men and women. In men, the longitudinal rate at which BP changed over time, however, did not generally parallel that of PWV acceleration: at ages above 40 years the rates of change in SBP and PP increase plateaued and then declined so that SBP, itself, also declined at older ages while PP plateaued. In women, SBP, DBP and MBP increased at constant rates across all ages, producing an increasing rate of increase in PP. Therefore, increased aortic stiffness is implicated in the age-associated increase in SBP and PP. These findings indicate that PWV is not a surrogate for BP and that arterial properties other than arterial wall stiffness that vary by age and sex also modulate the BP trajectories during aging and lead to the dissociation of PWV, PP and SBP trajectories in men. PMID:25225210
Inouye, Joshua M; Valero-Cuevas, Francisco J
2016-02-01
Much debate has arisen from research on muscle synergies with respect to both limb impedance control and energy consumption. Studies of limb impedance control in the context of reaching movements and postural tasks have produced divergent findings, and this study explores whether the use of synergies by the central nervous system (CNS) can resolve these findings and also provide insights on mechanisms of energy consumption. In this study, we phrase these debates at the conceptual level of interactions between neural degrees of freedom and tasks constraints. This allows us to examine the ability of experimentally-observed synergies-correlated muscle activations-to control both energy consumption and the stiffness component of limb endpoint impedance. In our nominal 6-muscle planar arm model, muscle synergies and the desired size, shape, and orientation of endpoint stiffness ellipses, are expressed as linear constraints that define the set of feasible muscle activation patterns. Quadratic programming allows us to predict whether and how energy consumption can be minimized throughout the workspace of the limb given those linear constraints. We show that the presence of synergies drastically decreases the ability of the CNS to vary the properties of the endpoint stiffness and can even preclude the ability to minimize energy. Furthermore, the capacity to minimize energy consumption-when available-can be greatly affected by arm posture. Our computational approach helps reconcile divergent findings and conclusions about task-specific regulation of endpoint stiffness and energy consumption in the context of synergies. But more generally, these results provide further evidence that the benefits and disadvantages of muscle synergies go hand-in-hand with the structure of feasible muscle activation patterns afforded by the mechanics of the limb and task constraints. These insights will help design experiments to elucidate the interplay between synergies and the mechanisms of learning, plasticity, versatility and pathology in neuromuscular systems. PMID:26867014
Longitudinal perspective on the conundrum of central arterial stiffness, blood pressure, and aging.
Scuteri, Angelo; Morrell, Christopher H; Orr, Marco; Strait, James B; Tarasov, Kirill V; Ferreli, Liana Anna Pina; Loi, Francesco; Pilia, Maria Grazia; Delitala, Alessandro; Spurgeon, Harold; Najjar, Samer S; AlGhatrif, Majd; Lakatta, Edward G
2014-12-01
The age-associated increase in arterial stiffness has long been considered to parallel or to cause the age-associated increase in blood pressure (BP). Yet, the rates at which pulse wave velocity (PWV), a measure of arterial stiffness, and BP trajectories change over time within individuals who differ by age and sex have not been assessed and compared. This study determined the evolution of BP and aortic PWV trajectories during a 9.4-year follow-up in >4000 community-dwelling men and women of 20 to 100 years of age at entry into the SardiNIA Study. Linear mixed effects model analyses revealed that PWV accelerates with time during the observation period, at about the same rate over the entire age range in both men and women. In men, the longitudinal rate at which BP changed over time, however, did not generally parallel that of PWV acceleration: at ages>40 years the rates of change in systolic BP (SBP) and pulse pressure (PP) increase plateaued and then declined so that SBP, itself, also declined at older ages, whereas PP plateaued. In women, SBP, diastolic BP, and mean BP increased at constant rates across all ages, producing an increasing rate of increase in PP. Therefore, increased aortic stiffness is implicated in the age-associated increase in SBP and PP. These findings indicate that PWV is not a surrogate for BP and that arterial properties other than arterial wall stiffness that vary by age and sex also modulate the BP trajectories during aging and lead to the dissociation of PWV, PP, and SBP trajectories in men. PMID:25225210
Inouye, Joshua M.; Valero-Cuevas, Francisco J.
2016-01-01
Much debate has arisen from research on muscle synergies with respect to both limb impedance control and energy consumption. Studies of limb impedance control in the context of reaching movements and postural tasks have produced divergent findings, and this study explores whether the use of synergies by the central nervous system (CNS) can resolve these findings and also provide insights on mechanisms of energy consumption. In this study, we phrase these debates at the conceptual level of interactions between neural degrees of freedom and tasks constraints. This allows us to examine the ability of experimentally-observed synergies—correlated muscle activations—to control both energy consumption and the stiffness component of limb endpoint impedance. In our nominal 6-muscle planar arm model, muscle synergies and the desired size, shape, and orientation of endpoint stiffness ellipses, are expressed as linear constraints that define the set of feasible muscle activation patterns. Quadratic programming allows us to predict whether and how energy consumption can be minimized throughout the workspace of the limb given those linear constraints. We show that the presence of synergies drastically decreases the ability of the CNS to vary the properties of the endpoint stiffness and can even preclude the ability to minimize energy. Furthermore, the capacity to minimize energy consumption—when available—can be greatly affected by arm posture. Our computational approach helps reconcile divergent findings and conclusions about task-specific regulation of endpoint stiffness and energy consumption in the context of synergies. But more generally, these results provide further evidence that the benefits and disadvantages of muscle synergies go hand-in-hand with the structure of feasible muscle activation patterns afforded by the mechanics of the limb and task constraints. These insights will help design experiments to elucidate the interplay between synergies and the mechanisms of learning, plasticity, versatility and pathology in neuromuscular systems. PMID:26867014
A piezoelectric-based infinite stiffness generation method for strain-type load sensors
NASA Astrophysics Data System (ADS)
Zhang, Shuwen; Shao, Shubao; Chen, Jie; Xu, Minglong
2015-11-01
Under certain application conditions like nanoindentation technology and the mechanical property measurement of soft materials, the elastic deformation of strain-type load sensors affects their displacement measurement accuracy. In this work, a piezoelectric-based infinite stiffness generation method for strain-type load sensors that compensates for this elastic deformation is presented. The piezoelectric material-based deformation compensation method is proposed. An Hottinger Baldwin Messtechnik GmbH (HBM) Z30A/50N load sensor acts as the foundation of the method presented in this work. The piezoelectric stack is selected based on its size, maximum deformation value, blocking force and stiffness. Then, a clamping and fixing structure is designed to integrate the HBM sensor with the piezoelectric stack. The clamping and fixing structure, piezoelectric stack and HBM load sensor comprise the sensing part of the enhanced load sensor. The load-deformation curve and the voltage-deformation curve of the enhanced load sensor are then investigated experimentally. Because a hysteresis effect exists in the piezoelectric structure, the relationship between the control signal and the deformation value of the piezoelectric material is nonlinear. The hysteresis characteristic in a quasi-static condition is studied and fitted using a quadratic polynomial, and its coefficients are analyzed to enable control signal prediction. Applied arithmetic based on current theory and the fitted data is developed to predict the control signal. Finally, the experimental effects of the proposed method are presented. It is shown that when a quasi-static load is exerted on this enhanced strain-type load sensor, the deformation is reduced and the equivalent stiffness appears to be almost infinite.
Dynamically tuned magnetostrictive spring with electrically controlled stiffness
NASA Astrophysics Data System (ADS)
Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.
2016-03-01
This paper presents the design and testing of an electrically controllable magnetostrictive spring that has a dynamically tunable stiffness (i.e., a magnetostrictive Varispring). The device enables in situ stiffness tuning or stiffness switching for vibration control applications. Using a nonlinear electromechanical transducer model and an analytical solution of linear, mechanically induced magnetic diffusion, Terfenol-D is shown to have a faster rise time to stepped voltage inputs and a significantly higher magnetic diffusion cut-off frequency relative to Galfenol. A Varispring is manufactured using a laminated Terfenol-D rod. Further rise time reductions are achieved by minimizing the rod’s diameter and winding the electromagnet with larger wire. Dynamic tuning of the Varispring’s stiffness is investigated by measuring the Terfenol-D rod’s strain response to dynamic, compressive, axial forces in the presence of sinusoidal or square wave control currents. The Varispring’s rise time is \\lt 1 ms for 1 A current switches. Continuous modulus changes up to 21.9 GPa and 500 Hz and square wave modulus changes (dynamic {{Δ }}E effect) up to 12.3 GPa and 100 Hz are observed. Stiffness tunability and tuning bandwidth can be considerably increased by operating about a more optimal bias stress and improving the control of the electrical input.
Arterial Stiffness, Kidney Function, and Chronic Kidney Disease Progression
Townsend, Raymond R.; Tomiyama, Hirofumi
2013-01-01
Arterial stiffness can nowadays be measured easily and noninvasively around the globe. Although well established as an independent predictor of cardiovascular events, less is known about the role of arterial stiffness in the progressive loss of kidney function once chronic kidney disease (CKD) is established. In addition to measures of arterial stiffness, a number of devices now noninvasively record the pulse profile from sites such as the radial artery and, using internal algorithms, are able to estimate central pressure profiles. Although these devices have generated much data on the prediction of cardiovascular events, e.g. measures of arterial stiffness, there is much less known about the predictive utility of these measures in CKD progression. In this review, we cover approaches to arterial stiffness as measured by pulse wave velocity and discuss measures of the systolic and diastolic contour of the pulse waveform vis--vis their relationship to declines in kidney function over time. We restrict our coverage to studies that have longitudinal data, but we also include a table of studies, which, to our knowledge, have only published cross-sectional data at this time. PMID:26587431
Stiffness Feedback for Myoelectric Forearm Prostheses Using Vibrotactile Stimulation.
Witteveen, Heidi J B; Luft, Frauke; Rietman, Johan S; Veltink, Peter H
2014-01-01
The ability to distinguish object stiffness is a very important aspect in object handling, but completely lacking in current myoelectric prostheses. In human hands both tactile and proprioceptive sensory information are required for stiffness determination. Therefore, it was investigated whether it is possible to distinguish object stiffness with vibrotactile feedback of hand opening and grasping force. Three configurations consisting of an array of coin motors and a single miniature vibrotactile transducer were investigated. Ten healthy subjects and seven subjects with upper limb loss due to amputation or congenital defects performed virtual grasping tasks, in which they controlled hand opening and grasping force. They were asked to determine the stiffness of a grasped virtual object from four options. With hand opening feedback alone or in combination with grasping force feedback, correct stiffness determination was achieved in around 60% of the cases and significantly higher than the 25% achieved without feedback or grasping force feedback alone. Despite the equal performance results, the combination of hand opening and grasping force feedback was preferred by the subjects over the hand opening feedback alone. No differences between feedback configurations and between subjects with upper limb loss and healthy subjects were found. PMID:23799698
Acute Achilles tendinopathy: effect of pain control on leg stiffness.
Maquirriain, J; Kokalj, A
2014-03-01
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. The aim of this study was to evaluate the effect of NSAIDs on leg stiffness of patients suffering acute unilateral Achilles tendinopathy. Twenty-eight eligible male athletes (aged 39.1 10.3 y) suffering acute Achilles tendinopathy were treated with etoricoxib (120 mg oral once daily) during 7 days. Pain (100-mm visual analogue scale-VAS), analgesic effect (percentage of 100-mm VAS reduction), and leg stiffness were evaluated pre- and post- anti-inflammatory treatment. Results of this study showed that over the 7-day treatment period, etoricoxib provided significant relief of Achilles tendon pain (VAS) compared to that experienced at baseline: 54.5 21.6 and 24.5 24.8, respectively (p<0.001). Leg stiffness showed a significant improvement after one-week NSAID therapy: LSR 0.89 0.1 vs. 0.97 0.1; (p=0.02). In conclusion, findings of this study demonstrated that patients suffering acute unilateral Achilles tendinopathy increased their leg stiffness of the affected side after oral anti-inflammatory therapy. Effective control of tendon pain in the acute phase of such sports-related injuries may contribute to improve capabilities associated with high performance like leg stiffness. PMID:24583548
Measuring Ascending Aortic Stiffness In Vivo in Mice Using Ultrasound
Kuo, Maggie M.; Barodka, Viachaslau; Abraham, Theodore P.; Steppan, Jochen; Shoukas, Artin A.; Butlin, Mark; Avolio, Alberto; Berkowitz, Dan E.; Santhanam, Lakshmi
2014-01-01
We present a protocol for measuring in vivo aortic stiffness in mice using high-resolution ultrasound imaging. Aortic diameter is measured by ultrasound and aortic blood pressure is measured invasively with a solid-state pressure catheter. Blood pressure is raised then lowered incrementally by intravenous infusion of vasoactive drugs phenylephrine and sodium nitroprusside. Aortic diameter is measured for each pressure step to characterize the pressure-diameter relationship of the ascending aorta. Stiffness indices derived from the pressure-diameter relationship can be calculated from the data collected. Calculation of arterial compliance is described in this protocol. This technique can be used to investigate mechanisms underlying increased aortic stiffness associated with cardiovascular disease and aging. The technique produces a physiologically relevant measure of stiffness compared to ex vivo approaches because physiological influences on aortic stiffness are incorporated in the measurement. The primary limitation of this technique is the measurement error introduced from the movement of the aorta during the cardiac cycle. This motion can be compensated by adjusting the location of the probe with the aortic movement as well as making multiple measurements of the aortic pressure-diameter relationship and expanding the experimental group size. PMID:25489936
Pharmacological bronchodilation is partially mediated by reduced airway wall stiffness
Ansell, T K; Noble, P B; Mitchell, H W; McFawn, P K
2014-01-01
Background and Purpose In asthmatic patients, airflow limitation is at least partly reversed by administration of pharmacological bronchodilators, typically β2-adrenoceptor agonists. In addition to receptor-mediated bronchodilation, the dynamic mechanical environment of the lung itself can reverse bronchoconstriction. We have now explored the possibility that bronchodilators exert a synergistic effect with oscillatory loads by virtue of reducing airway wall stiffness, and therefore, enhancing the bronchodilatory response to breathing manoeuvres. Experimental Approach Whole porcine bronchial segments in vitro were contracted to carbachol and relaxed to the non-specific β-adrenoceptor agonist, isoprenaline, under static conditions or during simulated breathing manoeuvres. Key Results The bronchodilatory response to isoprenaline was greater during breathing manoeuvres compared with the response under static conditions. As the bronchodilatory response to breathing manoeuvres is dependent upon airway smooth muscle (ASM) strain, and therefore, airway wall stiffness, our findings are likely to be explained by the effect of isoprenaline on reducing airway wall stiffness, which increased ASM strain, producing greater bronchodilation. Conclusions and Implications A contribution of reduced airway stiffness and increased ASM strain to the bronchodilator action of isoprenaline is shown, suggesting that oscillatory loads act synergistically with pharmacologically mediated bronchodilation. The implications for the treatment of asthma are that reducing airway wall stiffness represents a potential target for novel pharmacological agents. PMID:24846164
FIDAP capabilities for solving problems with stiff chemistry
Torczynski, J.R.; Baer, T.A.
1996-09-01
In support of the Motorola CRADA, the capabilities of the computational fluid dynamics code FIDAP (Fluid Dynamics International) for simulating problems involving fluid flow, heat transport, and chemical reactions have been assessed and enhanced as needed for semiconductor-processing applications (e.g. chemical vapor deposition). A novel method of treating surface chemical species that uses only pre-existing FIDAP commands is described and illustrated with test problems. A full-Jacobian treatment of the chemical reaction rate expressions during formation of the stiffness matrix has been implemented in FIDAP for both the Arrhenius-parameter and user-subroutine methods of specifying chemical reactions, where the Jacobian terms can be calculated analytically or numerically. This formulation is needed to obtain convergence when reaction rates become large compared to transport rates (stiff chemistry). Several test problems are analyzed, and in all cases this approach yields good convergence behavior, even for extremely stiff fluid-phase and surface reactions. A stiff segregated algorithm has been developed and implemented in FIDAP. Analysis of test problems indicates that this algorithm yields improved convergence behavior compared with the original segregated algorithm. This improved behavior enables segregated techniques to be applied to problems with stiff chemistry, as required for large three-dimensional multi-species problems.
Evaluating pulp stiffness from fibre bundles by ultrasound
NASA Astrophysics Data System (ADS)
Karppinen, Timo; Montonen, Risto; Mttnen, Marjo; Ekman, Axel; Myllys, Markko; Timonen, Jussi; Hggstrm, Edward
2012-06-01
A non-destructive ultrasonic tester was developed to measure the stiffness of pulp bundles. The mechanical properties of pulp are important when estimating the behaviour of paper under stress. Currently available pulp tests are tedious and alter the fibres structurally and mechanically. The developed tester employs (933 15) kHz tweezer-like ultrasonic transducers and time-of-flight measurement through (9.0 2.5) mm long and (0.8 0.1) mm thick fibre bundles kept at (19.1 0.4) C and (62 1)% RH. We determined the stiffness of soft wood pulps produced by three kraft pulping modifications: standard kraft pulp, (5.2 0.4) GPa, prehydrolysis kraft pulp, (4.3 0.4) GPa, and alkali extracted prehydrolysis kraft pulp, (3.3 0.4) GPa. Prehydrolysis and alkali extraction processes mainly lowered the hemicellulose content of the pulps, which essentially decreased the fibre-wall stiffness hence impairing the stiffness of the fibre networks. Our results indicate that the method allows ranking of pulps according to their stiffness determined from bundle-like samples taken at an early phase of the papermaking process.
Extended graphynes: simple scaling laws for stiffness, strength and fracture
NASA Astrophysics Data System (ADS)
Cranford, Steven W.; Brommer, Dieter B.; Buehler, Markus J.
2012-11-01
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.
Comparative Analysis of the Flexural Stiffness of Pinniped Vibrissae
Ginter Summarell, Carly C.; Ingole, Sudeep; Fish, Frank E.; Marshall, Christopher D.
2015-01-01
Vibrissae are important components of the mammalian tactile sensory system and are used to detect vibrotactile stimuli in the environment. Pinnipeds have the largest and most highly innervated vibrissae among mammals, and the hair shafts function as a biomechanical filter spanning the environmental stimuli and the neural mechanoreceptors deep in the follicle-sinus complex. Therefore, the material properties of these structures are critical in transferring vibrotactile information to the peripheral nervous system. Vibrissae were tested as cantilever beams and their flexural stiffness (EI) was measured to test the hypotheses that the shape of beaded vibrissae reduces EI and that vibrissae are anisotropic. EI was measured at two locations on each vibrissa, 25% and 50% of the overall length, and at two orientations to the point force. EI differed in orientations that were normal to each other, indicating a functional anisotropy. Since vibrissae taper from base to tip, the second moment of area (I) was lower at 50% than 25% of total length. The anterior orientation exhibited greater EI values at both locations compared to the dorsal orientation for all species. Smooth vibrissae were generally stiffer than beaded vibrissae. The profiles of beaded vibrissae are known to decrease the amplitude of vibrations when protruded into a flow field. The lower EI values of beaded vibrissae, along with the reduced vibrations, may function to enhance the sensitivity of mechanoreceptors to detection of small changes in flow from swimming prey by increasing the signal to noise ratio. This study builds upon previous morphological and hydrodynamic analyses of vibrissae and is the first comparative study of the mechanical properties of pinniped vibrissae. PMID:26132102
Extended graphynes: simple scaling laws for stiffness, strength and fracture.
Cranford, Steven W; Brommer, Dieter B; Buehler, Markus J
2012-12-21
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
NASA Technical Reports Server (NTRS)
Radhakrishnan, Krishnan; Bittker, David A.
1993-01-01
A general chemical kinetics and sensitivity analysis code for complex, homogeneous, gas-phase reactions is described. The main features of the code, LSENS, are its flexibility, efficiency and convenience in treating many different chemical reaction models. The models include static system, steady, one-dimensional, inviscid flow, shock initiated reaction, and a perfectly stirred reactor. In addition, equilibrium computations can be performed for several assigned states. An implicit numerical integration method, which works efficiently for the extremes of very fast and very slow reaction, is used for solving the 'stiff' differential equation systems that arise in chemical kinetics. For static reactions, sensitivity coefficients of all dependent variables and their temporal derivatives with respect to the initial values of dependent variables and/or the rate coefficient parameters can be computed. This paper presents descriptions of the code and its usage, and includes several illustrative example problems.
Double-smoothing for Varying Coefficient Models.
Tang, Wan; Zuo, Guoxin; He, Hua
2011-12-01
Moderation analyses are widely used in biomedical and psychosocial research to investigate differential treatment effects, with moderators frequently identified through testing the significance of the interaction between the predictor and the potential moderator under strong parametric assumptions. Without imposing any parametric forms on how the moderators may affect the relationship between predictors and responses, varying coefficient models address this fundamental problem of strong parametric assumptions with current practice of moderation analysis and provide a much broader class of models for complex moderation relationships. Local polynomial, especially local linear, methods are commonly used in estimating the varying coefficient models. Recently, a double-smoothing (DS) local linear method has been proposed for nonparametric regression models, with nice properties compared to local linear and local cubic methods. In this paper, we generalize DS to varying coefficient models, and show that it holds similar advantages over local linear and local cubic methods. PMID:22121327
Jang, Dae-Geun; Park, Seung-Hun; Hahn, Minsoo
2015-01-01
In this paper, we propose a novel method for enhancing pulse contour analysis-based arterial stiffness estimation using a simple and low-complexity photoplethysmographic parameter (P2Ocd). The method first eliminates baseline wanders in the digital volume pulse (DVP) by applying a simple morphological filter. The filtered DVP signal is then transformed into a slope sum function signal to simplify the pulse peak detection process by enhancing the upslope of the DVP signal while suppressing its downslope. An adaptive thresholding scheme is applied to detect pulse peaks from the transformed signal. Pulse onsets are then identified as the minimum values between consecutive pulse peaks. The P2Ocd is finally calculated by dividing the time interval between the pulse peak and the pulse onset by the pulse length. In order to assess the agreement of the P2Ocd with an established technique, brachial-ankle pulse wave velocity, we performed Bland-Altman and correlation analyses. Furthermore, we evaluated the P2Ocd-based arterial stiffness estimation in terms of prediction accuracy (% error rate) and repeatability (coefficient of variation). The results show that the proposed measurement agrees well with the established technique and shows a high repeatability; it also has a better predictive accuracy than that of conventional methods. In addition, we show that the proposed parameter further improves the predictive accuracy by combining it with age. The proposed method is therefore highly applicable to small ubiquitous healthcare applications. PMID:25561448
Evaluation of fatigue life of CRM-reinforced SMA and its relationship to dynamic stiffness.
Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati; Koting, Suhana
2014-01-01
Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400 kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture. PMID:25050406
Evaluation of Fatigue Life of CRM-Reinforced SMA and Its Relationship to Dynamic Stiffness
Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati
2014-01-01
Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400?kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture. PMID:25050406
Active pneumatic vibration isolation system using negative stiffness structures for a vehicle seat
NASA Astrophysics Data System (ADS)
Danh, Le Thanh; Ahn, Kyoung Kwan
2014-02-01
In this paper, an active pneumatic vibration isolation system using negative stiffness structures (NSS) for a vehicle seat in low excitation frequencies is proposed, which is named as an active system with NSS. Here, the negative stiffness structures (NSS) are used to minimize the vibratory attraction of a vehicle seat. Owing to the time-varying and nonlinear behavior of the proposed system, it is not easy to build an accurate dynamic for model-based controller design. Thus, an adaptive intelligent backstepping controller (AIBC) is designed to manage the system operation for high-isolation effectiveness. In addition, an auxiliary control effort is also introduced to eliminate the effect of the unpredictable perturbations. Moreover, a radial basis function neural network (RBFNN) model is utilized to estimate the optimal gain of the auxiliary control effort. Final control input and the adaptive law for updating coefficients of the approximate series can be obtained step by step using a suitable Lyapunov function. Afterward, the isolation performance of the proposed system is assessed experimentally. In addition, the effectiveness of the designed controller for the proposed system is also compared with that of the traditional backstepping controller (BC). The experimental results show that the isolation effectiveness of the proposed system is better than that of the active system without NSS. Furthermore, the undesirable chattering phenomenon in control effort is quite reduced by the estimation mechanism. Finally, some concluding remarks are given at the end of the paper.
Quantifying molecular stiffness and interaction with lateral force microscopy.
Weymouth, Alfred John; Hofmann, Thomas; Giessibl, Franz J
2014-03-01
The spatial resolution of atomic force microscopy (AFM) can be drastically increased by terminating the tip with a single carbon monoxide (CO) molecule. However, the CO molecule is not stiff, and lateral forces, such as those around the sides of molecules, distort images. This issue begs a larger question of how AFM can probe structures that are laterally weak. Lateral force microscopy (LFM) can probe lateral stiffnesses that are not accessible to normal-force AFM, resulting in higher spatial resolution. With LFM, we determined the torsional spring constant of a CO-terminated tip molecule to be 0.24 newtons per meter. This value is less than that of a surface molecule and an example of a system whose stiffness is a product not only of bonding partners but also local environment. PMID:24505131
Effect of surface stress on the stiffness of cantilever plates.
Lachut, Michael J; Sader, John E
2007-11-16
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. PMID:18233163
Estimation of Stiffness Parameter on the Common Carotid Artery
NASA Astrophysics Data System (ADS)
Koya, Yoshiharu; Mizoshiri, Isao; Matsui, Kiyoaki; Nakamura, Takashi
The arteriosclerosis is on the increase with an aging or change of our living environment. For that reason, diagnosis of the common carotid artery using echocardiogram is doing to take precautions carebropathy. Up to the present, several methods to measure stiffness parameter of the carotid artery have been proposed. However, they have analyzed at the only one point of common carotid artery. In this paper, we propose the method of analysis extended over a wide area of common carotid artery. In order to measure stiffness parameter of common carotid artery from echocardiogram, it is required to detect two border curves which are boundaries between vessel wall and blood. The method is composed of two steps. The first step is the detection of border curves, and the second step is the calculation of stiffness parameter using diameter of common carotid artery. Experimental results show the validity of the proposed method.
Tissue Stiffness Dictates Development, Homeostasis, and Disease Progression
Handorf, Andrew M; Zhou, Yaxian; Halanski, Matthew A; Li, Wan-Ju
2015-01-01
Abstract Tissue development is orchestrated by the coordinated activities of both chemical and physical regulators. While much attention has been given to the role that chemical regulators play in driving development, researchers have recently begun to elucidate the important role that the mechanical properties of the extracellular environment play. For instance, the stiffness of the extracellular environment has a role in orienting cell division, maintaining tissue boundaries, directing cell migration, and driving differentiation. In addition, extracellular matrix stiffness is important for maintaining normal tissue homeostasis, and when matrix mechanics become imbalanced, disease progression may ensue. In this article, we will review the important role that matrix stiffness plays in dictating cell behavior during development, tissue homeostasis, and disease progression. PMID:25915734
An activity coefficient model for proteins.
Agena, S M; Bogle, I D; Pessoa, F L
1997-07-01
Modeling of the properties of biochemical components is gaining increasing interest due to its potential for further application within the area of biochemical process development. Generally protein solution properties such as protein solubility are expressed through component activity coefficients which are studied here. The original UNIQUAC model is chosen for the representation of protein activity coefficients and, to the best of our knowledge, this is the first time it has been directly applied to protein solutions. Ten different protein-salt-water systems with four different proteins, serum albumin, alphacymotrypsin, beta-lactoglobulin and ovalbumin, are investigated. A root-mean-squared deviation of 0.54% is obtained for the model by comparing calculated protein activity coefficients and protein activity coefficients deduced from osmotic measurements through virial expansion. Model predictions are used to analyze the effect of salt concentrations, pH, salt types, and temperature on protein activity coefficients and also on protein solubility and demonstrate consistency with results from other references. PMID:18636445
NASA Astrophysics Data System (ADS)
Zheng, Yisheng; Zhang, Xinong; Luo, Yajun; Yan, Bo; Ma, Chicheng
2016-01-01
To improve the vibration isolation performance under low frequency excitation, a negative stiffness magnetic spring (NSMS) is employed to reduce the resonance frequency of the linear isolator. The NSMS comprising a pair of coaxial ring permanent magnets is installed in parallel with the mechanical spring to counteract its positive stiffness. The major feature of the isolator is that it has high static low dynamic stiffness (HSLDS). In this paper, the model of the HSLDS isolator and the NSMS is analyzed firstly; and the magnetic force and stiffness exerted between the inner magnet and the outer magnet is then calculated based on the Amperian current model. After analyzing the effect of the geometric parameters of the magnets on the stiffness characteristic of the NSMS, a designing procedure for the NSMS is proposed. Then the nonlinear dynamic equation of the isolator is established and numerical simulation is performed to obtain the transmissibility. Finally, the detailed design of the HSLDS isolator is given and an experimental setup is proposed. The experimental results demonstrate that the NSMS can reduce the resonance frequency of the isolator indeed; and the isolation performance of the proposed isolator is improved accordingly.
Time-varying torsional stiffness identification on a vertical beam using Chebyshev polynomials
NASA Astrophysics Data System (ADS)
Martel, Franois; Rancourt, Denis; Chochol, Catherine; St-Amant, Yves; Chesne, Simon; Rmond, Didier
2015-03-01
This paper investigates the performance of the Chebyshev polynomial basis to identify the time-varying mechanical impedance of a vertical beam in torsion. The projection, derivation and product properties of Chebyshev polynomials were used to linearize the differential equation of 1-DOF mechanical systems having multiple time-varying parameters. This allowed the identification of a reduced set of projection coefficients without prior knowledge of initial system states conditions. The method was then applied to experimental data obtained from an equilateral beam excited in torsion while one beam support location was changed over time. Results showed 6.6210-2% error in stiffness predictions compared to theoretical estimates. Signal filtering was critical to avoid contamination by bending modes of the beam and prior knowledge of inertia led to better results.
Computational methods for the identification of spatially varying stiffness and damping in beams
NASA Technical Reports Server (NTRS)
Banks, H. T.; Rosen, I. G.
1986-01-01
A numerical approximation scheme for the estimation of functional parameters in Euler-Bernoulli models for the transverse vibration of flexible beams with tip bodies is developed. The method permits the identification of spatially varying flexural stiffness and Voigt-Kelvin viscoelastic damping coefficients which appear in the hybrid system of ordinary and partial differential equations and boundary conditions describing the dynamics of such structures. An inverse problem is formulated as a least squares fit to data subject to constraints in the form of a vector system of abstract first order evolution equations. Spline-based finite element approximations are used to finite dimensionalize the problem. Theoretical convergence results are given and numerical studies carried out on both conventional (serial) and vector computers are discussed.
Lee, Yunju; Ashton-Miller, James A
2015-05-01
Whether an arm will buckle under an impulsive end-load should partly depend on the elastic and viscous properties of the pretensed arm muscles. In measuring these properties we hypothesized that neither age, gender, nor muscle pre-contraction level would affect the bilinear elbow or shoulder lumped rotational stiffness or damping parameters in the impulsively end-loaded upper extremity of 38 healthy men and women. Subjects were instructed to preactivate triceps to either 25, 50 or 75% of maximum myoelectric activity levels. Then a standardized impulsive end-load was applied via a 6-axis load cell to the wrist of the slightly flexed arm in the prone posture. Arm kinematic responses were acquired at 280Hz and an inverse dynamics analysis was used to estimate the bilinear rotational stiffnesses and damping parameters at the elbow and shoulder. The results show that pre-contraction level affected normalized joint rotational stiffness and damping coefficients (p<0.02). Age affected the initial stiffness for the elbow (p<0.05), and gender affected that of the shoulder in the sagittal plane (p<0.006). Arm muscle strength was positively related to normalized stiffness at the elbow, but not the shoulder. We conclude that age, gender and pre-contraction level each affect the viscoelastic behavior of the end-loaded upper extremity in healthy adults. PMID:25395216
NASA Astrophysics Data System (ADS)
Weber, F.; Distl, H.
2015-11-01
This paper derives an approximate collocated control solution for the mitigation of multi-mode cable vibration by semi-active damping with negative stiffness based on the control force characteristics of clipped linear quadratic regulator (LQR). The control parameters are derived from optimal modal viscous damping and corrected in order to guarantee that both the equivalent viscous damping coefficient and the equivalent stiffness coefficient of the semi-active cable damper force are equal to their desired counterparts. The collocated control solution with corrected control parameters is numerically validated by free decay tests of the first four cable modes and combinations of these modes. The results of the single-harmonic tests demonstrate that the novel approach yields 1.86 times more cable damping than optimal modal viscous damping and 1.87 to 2.33 times more damping compared to a passive oil damper whose viscous damper coefficient is optimally tuned to the targeted mode range of the first four modes. The improvement in case of the multi-harmonic vibration tests, i.e. when modes 1 and 3 and modes 2 and 4 are vibrating at the same time, is between 1.55 and 3.81. The results also show that these improvements are obtained almost independent of the cable anti-node amplitude. Thus, the proposed approximate real-time applicable collocated semi-active control solution which can be realized by magnetorheological dampers represents a promising tool for the efficient mitigation of stay cable vibrations.
Further understanding of Huygens’ coupled clocks: The effect of stiffness
NASA Astrophysics Data System (ADS)
Peña Ramirez, J.; Aihara, K.; Fey, R. H. B.; Nijmeijer, H.
2014-03-01
A simplified model of the classical Huygens’ experiment on synchronization of pendulum clocks is examined. The model consists of two pendula coupled by an elastically supported rigid bar. The synchronized limit behaviour of the system, i.e. in-phase and anti-phase synchronization of the pendula, is studied as a function of the stiffness of the spring that supports the coupling bar. It is demonstrated that the stiffness has a large influence on the existence, stability, and oscillation frequency of the in-phase solution. The relationship between the obtained results and experimental results that have been reported in the literature, including Huygens’ original observations, is stressed.
Fuzzy evaluation of stiffness of tissue by means of micromanipulator
NASA Astrophysics Data System (ADS)
Majima, Sumiko; Matsushima, Kozo
1993-09-01
We have developed a bilateral controlled remote micro-manipulator system for medical application. By operating this system an opretor can perceive the stiffness of small part of tissue with his/her tactile sense and the visco-elastic parameters of the tissue are identified from the measerments of the displacement and the reaction force on the slave manipulator. Firstly the relation between the tactile sense and the identified viscoelastic parameters is experimentally obtained. And then using this relation a method which evaluates the stiffness of the tissue by means of the fuzzy reasoning is proposed.
Thermal Testing of Tow-Placed, Variable Stiffness Panels
NASA Technical Reports Server (NTRS)
Wu, K. Chauncey; Guerdal, Zafer
2001-01-01
Commercial systems for precise placement of pre-preg composite tows are enabling technology that allows fabrication of advanced composite structures in which the tows may be precisely laid down along curvilinear paths within a given ply. For laminates with curvilinear tow paths, the fiber orientation angle varies continuously throughout the laminate, and is not required to be straight and parallel in each ply as in conventional composite laminates. Hence, the stiffness properties vary as a function of location in the laminate, and the associated composite structure is called a "variable stiffness" composite structure.
Effect of Hybridization on Stiffness Properties of Woven Textile Composites
NASA Astrophysics Data System (ADS)
Bejan, Liliana; Taranu, Nicolae; Srbu, Adriana
2013-04-01
The present study focuses on stiffness properties of woven textile reinforced polymeric composites with respect to hybridization, and geometry of reinforcement. The analyzed composites represent combinations of different fibre materials (E-glass, Kevlar 49, carbon HM) in a predetermined fabric geometry (a plane weave embedded in thermosetting polymeric resin) serving controlled properties and required performance. The effects of hybridization on the stiffness properties of woven textile composites have been studied with respect to the fibres materials, the unbalancing degree of fabrics, and the variation of compactness and undulation of yarns. Some undesirable effects in fabric geometry can be overcome by the combined effects of hybridization and compactness.
Stiffness measurement using terahertz and acoustic waves for biological samples.
Yoon, Jong-Hyun; Yang, Young-Joong; Park, Jinho; Son, Heyjin; Park, Hochong; Park, Gun-Sik; Ahn, Chang-Beom
2015-12-14
A method is proposed to measure sample stiffness using terahertz wave and acoustic stimulation. The stiffness-dependent vibration is measured using terahertz wave (T-ray) during an acoustic stimulation. To quantify the vibration, time of the peak amplitude of the reflected T-ray is measured. In our experiment, the T-ray is asynchronously applied during the period of the acoustic stimulation, and multiple measurements are taken to use the standard deviation and the maximum difference in the peak times to estimate the amplitude of the vibration. Some preliminary results are shown using biological samples. PMID:26699056
Influence of substrate stiffness on the phenotype of heart cells.
Bhana, Bashir; Iyer, Rohin K; Chen, Wen Li Kelly; Zhao, Ruogang; Sider, Krista L; Likhitpanichkul, Morakot; Simmons, Craig A; Radisic, Milica
2010-04-15
Adult cardiomyocytes (CM) retain little capacity to regenerate, which motivates efforts to engineer heart tissues that can emulate the functional and mechanical properties of native myocardium. Although the effects of matrix stiffness on individual CM have been explored, less attention was devoted to studies at the monolayer and the tissue level. The purpose of this study was to characterize the influence of substrate mechanical stiffness on the heart cell phenotype and functional properties. Neonatal rat heart cells were seeded onto collagen-coated polyacrylamide (PA) substrates with Young's moduli of 3, 22, 50, and 144 kPa. Collagen-coated glass coverslips without PA represented surfaces with effectively "infinite" stiffness. The local elastic modulus of native neonatal rat heart tissue was measured to range from 4.0 to 11.4 kPa (mean value of 6.8 kPa) and for native adult rat heart tissue from 11.9 to 46.2 kPa (mean value of 25.6 kPa), motivating our choice of the above PA gel stiffness. Overall, by 120 h of cultivation, the lowest stiffness PA substrates (3 kPa) exhibited the lowest excitation threshold (ET; 3.5 +/- 0.3 V/cm), increased troponin I staining (52% positively stained area) but reduced cell density, force of contraction (0.18 +/- 0.1 mN/mm(2)), and cell elongation (aspect ratio = 1.3-1.4). Higher stiffness (144 kPa) PA substrates exhibited reduced troponin I staining (30% positively stained area), increased fibroblast density (70% positively stained area), and poor electrical excitability. Intermediate stiffness PA substrates of stiffness comparable to the native adult rat myocardium (22-50 kPa) were found to be optimal for heart cell morphology and function, with superior elongation (aspect ratio > 4.3), reasonable ET (ranging from 3.95 +/- 0.8 to 4.4 +/- 0.7 V/cm), high contractile force development (ranging from 0.52 +/- 0.2 to 1.60 +/- 0.6 mN/mm(2)), and well-developed striations, all consistent with a differentiated phenotype. PMID:20014437
Symmetry chains and adaptation coefficients
Fritzer, H.P.; Gruber, B.
1985-06-01
Given a symmetry chain of physical significance it becomes necessary to obtain states which transform properly with respect to the symmetries of the chain. In this article we describe a method which permits us to calculate symmetry-adapted quantum states with relative ease. The coefficients for the symmetry-adapted linear combinations are obtained, in numerical form, in terms of the original states of the system and can thus be represented in the form of numerical tables. In addition, one also obtains automatically the matrix elements for the operators of the symmetry groups which are involved, and thus for any physical operator which can be expressed either as an element of the algebra or of the enveloping algebra. The method is well suited for computers once the physically relevant symmetry chain, or chains, have been defined. While the method to be described is generally applicable to any physical system for which semisimple Lie algebras play a role we choose here a familiar example in order to illustrate the method and to illuminate its simplicity. We choose the nuclear shell model for the case of two nucleons with orbital angular momentum l = 1. While the states of the entire shell transform like the smallest spin representation of SO(25) we restrict our attention to its subgroup SU(6) x SU(2)/sub T/. We determine the symmetry chains which lead to total angular momentum SU(2)/sub J/ and obtain the symmetry-adapted states for these chains.
Analytic properties of Hansen coefficients
NASA Astrophysics Data System (ADS)
Sadov, Sergey Yu.
2008-04-01
Hansen’s coefficients in the theory of elliptic motion with eccentricity e are studied as functions of the parameter η = (1 - e 2)1/2. Their analytic behavior in the complex η plane is described and some symmetry relations are derived. In particular, for every Hansen coefficient, multiplication by suitable powers of e and η results in an entire analytic function of η. Consequently, Hansen’s coefficients can be in principle computed by means of rapidly convergent series in powers of η. A representation of Hansen’s coefficients in terms of two entire functions of e 2 follows.
Coefficient Alpha: A Reliability Coefficient for the 21st Century?
ERIC Educational Resources Information Center
Yang, Yanyun; Green, Samuel B.
2011-01-01
Coefficient alpha is almost universally applied to assess reliability of scales in psychology. We argue that researchers should consider alternatives to coefficient alpha. Our preference is for structural equation modeling (SEM) estimates of reliability because they are informative and allow for an empirical evaluation of the assumptions
Factor Scores, Structure and Communality Coefficients: A Primer
ERIC Educational Resources Information Center
Odum, Mary
2011-01-01
(Purpose) The purpose of this paper is to present an easy-to-understand primer on three important concepts of factor analysis: Factor scores, structure coefficients, and communality coefficients. Given that statistical analyses are a part of a global general linear model (GLM), and utilize weights as an integral part of analyses (Thompson, 2006;
Flexural stiffnesses of and dimensional stability in circular quasi-isotropic laminate mirrors
NASA Astrophysics Data System (ADS)
Kim, Kyung-Pyo
Composite fiber reinforced plastics are being given favorable consideration for emerging applications in large aperture telescopes, such as the Hubble telescope or communication dishes. Many lightweight mirror fabrication concepts are currently being pursued. Presently, the technology is limited because it has an incomplete understanding of the mechanics associated with quasi-isotropic laminates for diffraction-limited displacement constraints, and lack of understanding for effects of resin buffer layers on composite mirrors for high surface smoothness. In this dissertation document, radial stiffness associated with stacking sequence effects in quasi-isotropic laminates (pi/n, where n=3, 4, and 6) and dimensional stability in the composite laminates are investigated numerically. The numerical results show that directional dependency of flexural stiffness in the laminates, which is strongly associated with stacking sequences, is a significant factor causing unfavorable sinusoidal surface waviness. The maximum radial flexural stiffness variation is found as +/-12.85% in pi/3 laminate while a minimum of +/-5.63% is found in pi/4 laminate. Mechanics of maximum asymmetry by +/-2 misorientation based on ideal pi/n laminate lay-ups are evaluated and the results are compared with ideal lay-up sequence cases. The calculated extensional and flexural stiffness values from the maximum asymmetric cases are within less than 0.05%. As such, the radial flexural stiffness variations in quasi-isotropic laminates are shown to be more problematic than asymmetry caused by common manufacturing variance. The types of surface deformations in quasi-isotropic laminates associated with directional dependency of flexural stiffness are evaluated using finite element analyses. Also, fiber print-through in replicated composite mirrors and the effects of the resin buffer layer present in the mirrors for mitigation of the fiber print-through are investigated and discussed. Numerical results reveal that there will be an unfavorable sinusoidal surface deformation in each ideal p/n laminate and the shapes are strongly associated with principal fiber directions due to stacking sequence effects. The surface deformations in quasi-isotropic laminates are shown to be typical and such surface deformations are inevitable when composite mirrors are fabricated from discrete layers of anisotropic carbon fiber reinforced plastics. Moreover, the use of additional resin layers appears to more adversely influence the composite mirror substrates. The validation of predicted surface deformations and dimensional distortions are achieved by comparing experimental results on a 8-inch-diameter composite mirror sample fabricated at the University of Kansas Dept. of Aerospace Engineering (KUAE) and Bennett Optical Research (BOR). A study of quasi-homogeneous materials such as short fiber products as alternative composite materials is investigated. Furthermore, the relation between resin property effects and corresponding resin thickness effects is evaluated and discussed. The analyses provide information on alternative types of materials that primarily affect optical performance and thus are most important for precision optics. Based on the results, locally varying radial surface deformations in quasi-isotropic laminates fabricated from continuous fiber reinforced plastics distort optical performance. These surface deformations might be eliminated by utilizing short fiber materials and a soft resin system with a very low coefficient of thermal expansion compared to conventional resins.
Satoh, Hiroki; Kishi, Reiko; Tsutsui, Hiroyuki
2009-12-01
Metabolic syndrome (MetS) has been recognized as a risk factor for cardiovascular disease; however, the impact of MetS on arterial stiffness has not been fully established in the general Japanese population. We analyzed the relationship between MetS and the severity of arterial stiffness using brachial-ankle pulse wave velocity (baPWV) in 2744 male and 358 female subjects aged 38-62 years, adjusted for conventional risk factors and C-reactive protein. The prevalence rates of MetS identified by Japanese criteria were 22.7% (n=624) and 7.8% (n=28) in male and female subjects, respectively. The subjects with MetS had significantly greater mean values of baPWV than those without MetS among both male and female subjects (1444+/-209 vs. 1294+/-165 cm/s in male subjects, P<0.001; 1379+/-151 vs. 1220+/-171 cm/s in female subjects, P<0.001). After adjustment for atherosclerotic variables such as age, smoking habits, total cholesterol and C-reactive protein, the odds ratio (OR) of MetS for increased baPWV was 3.65 in male subjects (95% confidence interval (CI): 2.99-4.47, P<0.001) and 8.02 in female subjects (95% CI: 3.18-20.25 P<0.001). In conclusion, MetS was identified as a significant and independent risk factor for increased arterial stiffness in both the male and female general population in Japan. PMID:19779485
Extracellular matrix stiffness dictates Wnt expression through integrin pathway
Du, Jing; Zu, Yan; Li, Jing; Du, Shuyuan; Xu, Yipu; Zhang, Lang; Jiang, Li; Wang, Zhao; Chien, Shu; Yang, Chun
2016-01-01
It is well established that extracellular matrix (ECM) stiffness plays a significant role in regulating the phenotypes and behaviors of many cell types. However, the mechanism underlying the sensing of mechanical cues and subsequent elasticity-triggered pathways remains largely unknown. We observed that stiff ECM significantly enhanced the expression level of several members of the Wnt/β-catenin pathway in both bone marrow mesenchymal stem cells and primary chondrocytes. The activation of β-catenin by stiff ECM is not dependent on Wnt signals but is elevated by the activation of integrin/ focal adhesion kinase (FAK) pathway. The accumulated β-catenin then bound to the wnt1 promoter region to up-regulate the gene transcription, thus constituting a positive feedback of the Wnt/β-catenin pathway. With the amplifying effect of positive feedback, this integrin-activated β-catenin/Wnt pathway plays significant roles in mediating the enhancement of Wnt signal on stiff ECM and contributes to the regulation of mesenchymal stem cell differentiation and primary chondrocyte phenotype maintenance. The present integrin-regulated Wnt1 expression and signaling contributes to the understanding of the molecular mechanisms underlying the regulation of cell behaviors by ECM elasticity. PMID:26854061
Variable Stiffness Spar Wind-Tunnel Model Development and Testing
NASA Technical Reports Server (NTRS)
Florance, James R.; Heeg, Jennifer; Spain, Charles V.; Ivanco, Thomas G.; Wieseman, Carol D.; Lively, Peter S.
2004-01-01
The concept of exploiting wing flexibility to improve aerodynamic performance was investigated in the wind tunnel by employing multiple control surfaces and by varying wing structural stiffness via a Variable Stiffness Spar (VSS) mechanism. High design loads compromised the VSS effectiveness because the aerodynamic wind-tunnel model was much stiffer than desired in order to meet the strength requirements. Results from tests of the model include stiffness and modal data, model deformation data, aerodynamic loads, static control surface derivatives, and fuselage standoff pressure data. Effects of the VSS on the stiffness and modal characteristics, lift curve slope, and control surface effectiveness are discussed. The VSS had the most effect on the rolling moment generated by the leading-edge outboard flap at subsonic speeds. The effects of the VSS for the other control surfaces and speed regimes were less. The difficulties encountered and the ability of the VSS to alter the aeroelastic characteristics of the wing emphasize the need for the development of improved design and construction methods for static aeroelastic models. The data collected and presented is valuable in terms of understanding static aeroelastic wind-tunnel model development.
Influence of passive stiffness of hamstrings on postural stability.
Kuszewski, Micha?; Gnat, Rafa?; Sobota, Grzegorz; My?liwiec, Andrzej
2015-03-29
The aim of the study was to explore whether passive stiffness of the hamstrings influences the strategy of maintaining postural stability. A sample of 50 subjects was selected; the final analyses were based on data of 41 individuals (33 men, 8 women) aged 21 to 29 (mean = 23.3, SD = 1.1) years. A quasi- experimental ex post facto design with repeated measures was used. Categories of independent variables were obtained directly prior to the measurement of the dependent variables. In stage one of the study, passive knee extension was measured in the supine position to assess hamstring stiffness. In stage two, the magnitude of postural sway in antero-posterior direction was measured, while varying the body position on a stabilometric platform, both with and without visual control. The margin of safety was used as a measure of postural control. The magnitude of the margin of safety increased significantly between the open-eye and closed-eye trials. However, although we registered a visible tendency for a larger increase of the margin of safety associated with lower levels of passive hamstrings stiffness, no significant differences were found. Therefore, this study demonstrated that hamstring stiffness did not influence the strategy used to maintain postural stability. PMID:25964809
A torsion quasi-zero stiffness vibration isolator
NASA Astrophysics Data System (ADS)
Zhou, Jiaxi; Xu, Daolin; Bishop, Steven
2015-03-01
A torsion vibration isolator with quasi-zero stiffness (QZS) is proposed to attenuate the transmission of torsional vibration along a shaft system, which also plays a role of coupling between shafts. A pre-compressed cam-roller mechanism is designed to provide torsional negative stiffness that counteracts with the positive torsion stiffness of the vulcanized rubber between shafts. With the design parameters are set to satisfy a unique condition, the stiffness of the isolator delivers a QZS property about the equilibrium position. A nonlinear mathematical model is developed and its dynamic characteristics are further analyzed by using the Harmonic Balance method. A typical folded resonance curve occurs when the vibration amplitude is plotted as the excitation frequency is varied, illustrating a jump phenomenon in the response. The efficiency of vibration attenuation is estimated under a designed torque load, showing that the torsion QZS vibration isolator outperforms the corresponding linear counterpart, especial in low frequency ranges. Furthermore, the torque transmissibility of the QZS isolator is also studied to demonstrate the performance of the QZS isolator when the actual torque deviates from the design load.
Initial post-buckling of variable-stiffness curved panels
NASA Astrophysics Data System (ADS)
White, S. C.; Raju, G.; Weaver, P. M.
2014-11-01
Variable-stiffness shells are curved composite structures in which the fibre-reinforcement follow curvilinear paths in space. Having a wider design space than traditional composite shells, they have the potential to improve a wide variety of weight-critical structures. In this paper, a new method for computing the initial post-buckling response of variable-stiffness cylindrical panels is presented, based on the differential quadrature method. Integro-differential governing and boundary equations governing the problem, derived with Koiter's theory (Koiter, 1945), are solved using a mixed generalised differential quadrature (GDQ) and integral quadrature (GIQ) approach. The post-buckling behaviour is determined on the basis of a quadratic expansion of the displacement fields. Orthogonality of the mode-shapes in the expansion series is ensured by a novel use of the Moore-Penrose generalised matrix inverse for solving the GDQ-GIQ equations. The new formulation is validated against benchmark analytical post-buckling results for constant stiffness plates and shells, and compared with non-linear finite-element (FE) analysis for variable-stiffness shells. Stability estimates are found to be in good agreement with incremental FE results in the vicinity of the buckling load, requiring only a fraction of the number of variables used by the current method.
Substrate stiffness affects skeletal myoblast differentiation in vitro
NASA Astrophysics Data System (ADS)
Romanazzo, Sara; Forte, Giancarlo; Ebara, Mitsuhiro; Uto, Koichiro; Pagliari, Stefania; Aoyagi, Takao; Traversa, Enrico; Taniguchi, Akiyoshi
2012-12-01
To maximize the therapeutic efficacy of cardiac muscle constructs produced by stem cells and tissue engineering protocols, suitable scaffolds should be designed to recapitulate all the characteristics of native muscle and mimic the microenvironment encountered by cells in vivo. Moreover, so not to interfere with cardiac contractility, the scaffold should be deformable enough to withstand muscle contraction. Recently, it was suggested that the mechanical properties of scaffolds can interfere with stem/progenitor cell functions, and thus careful consideration is required when choosing polymers for targeted applications. In this study, cross-linked poly-?-caprolactone membranes having similar chemical composition and controlled stiffness in a supra-physiological range were challenged with two sources of myoblasts to evaluate the suitability of substrates with different stiffness for cell adhesion, proliferation and differentiation. Furthermore, muscle-specific and non-related feeder layers were prepared on stiff surfaces to reveal the contribution of biological and mechanical cues to skeletal muscle progenitor differentiation. We demonstrated that substrate stiffness does affect myogenic differentiation, meaning that softer substrates can promote differentiation and that a muscle-specific feeder layer can improve the degree of maturation in skeletal muscle stem cells.
Arterial Stiffness Alterations and Inflammatory Response Following Endovascular Aortic Repair
Moulakakis, Konstantinos G.; Mylonas, Spyridon N.; Kakisis, John; Kadoglou, Nikolaos P.E.; Papadakis, Ioannis; Sfyroeras, George S.; Antonopoulos, Constantine C.N.; Mantas, George; Ikonomidis, Ignatios; Liapis, Christos D.
2015-01-01
Endovascular abdominal aortic aneurysm repair (EVAR) and thoracic aortic aneurysm repair (TEVAR) have been widely incorporated into clinical practice. However, changes in arterial stiffness and post-implantation syndrome after aortic endografting remain important issues under investigation. The aneurysm sac wall motion after successful EVAR and TEVAR reflects complex interactions between all the components of the excluded aneurysm, including true compliance of the aneurysm wall itself, intra-aneurysm sac pressure, remodeling of the thrombus, and mechanical characteristics of the endograft. Experimental and clinical studies have shown that aortic endografting results in increased arterial stiffness in animal models. It can be assumed that the alterations of aortic mechanical properties can have a direct impact on heart output. The long-term impact of these mechanical changes on cardiovascular outcomes and the potential effects of different endografts on hemodynamics are important issues under investigation. Post-implantation syndrome (PIS) is a systemic inflammatory response frequently observed after endovascular treatment of aortic pathologies. The main features of PIS include fever, leukocytosis, elevated C-reactive protein levels, and coagulation disturbances. Endograft design appears to influence this inflammatory response following aortic endografting; woven polyester endografts have been shown to be associated with greater inflammatory response compared to PTFE stent grafts. The purpose of this paper is to review the literature to elucidate arterial stiffness alterations and inflammatory response after EVAR and TEVAR and the impact of endograft design on aortic stiffness and the post-inflammatory response. PMID:26798761
Design optimization of a twist compliant mechanism with nonlinear stiffness
NASA Astrophysics Data System (ADS)
Tummala, Y.; Frecker, M. I.; Wissa, A. A.; Hubbard, J. E., Jr.
2014-10-01
A contact-aided compliant mechanism called a twist compliant mechanism (TCM) is presented in this paper. This mechanism has nonlinear stiffness when it is twisted in both directions along its axis. The inner core of the mechanism is primarily responsible for its flexibility in one twisting direction. The contact surfaces of the cross-members and compliant sectors are primarily responsible for its high stiffness in the opposite direction. A desired twist angle in a given direction can be achieved by tailoring the stiffness of a TCM. The stiffness of a compliant twist mechanism can be tailored by varying thickness of its cross-members, thickness of the core and thickness of its sectors. A multi-objective optimization problem with three objective functions is proposed in this paper, and used to design an optimal TCM with desired twist angle. The objective functions are to minimize the mass and maximum von-Mises stress observed, while minimizing or maximizing the twist angles under specific loading conditions. The multi-objective optimization problem proposed in this paper is solved for an ornithopter flight research platform as a case study, with the goal of using the TCM to achieve passive twisting of the wing during upstroke, while keeping the wing fully extended and rigid during the downstroke. Prototype TCMs have been fabricated using 3D printing and tested. Testing results are also presented in this paper.
Extracellular matrix stiffness dictates Wnt expression through integrin pathway.
Du, Jing; Zu, Yan; Li, Jing; Du, Shuyuan; Xu, Yipu; Zhang, Lang; Jiang, Li; Wang, Zhao; Chien, Shu; Yang, Chun
2016-01-01
It is well established that extracellular matrix (ECM) stiffness plays a significant role in regulating the phenotypes and behaviors of many cell types. However, the mechanism underlying the sensing of mechanical cues and subsequent elasticity-triggered pathways remains largely unknown. We observed that stiff ECM significantly enhanced the expression level of several members of the Wnt/?-catenin pathway in both bone marrow mesenchymal stem cells and primary chondrocytes. The activation of ?-catenin by stiff ECM is not dependent on Wnt signals but is elevated by the activation of integrin/ focal adhesion kinase (FAK) pathway. The accumulated ?-catenin then bound to the wnt1 promoter region to up-regulate the gene transcription, thus constituting a positive feedback of the Wnt/?-catenin pathway. With the amplifying effect of positive feedback, this integrin-activated ?-catenin/Wnt pathway plays significant roles in mediating the enhancement of Wnt signal on stiff ECM and contributes to the regulation of mesenchymal stem cell differentiation and primary chondrocyte phenotype maintenance. The present integrin-regulated Wnt1 expression and signaling contributes to the understanding of the molecular mechanisms underlying the regulation of cell behaviors by ECM elasticity. PMID:26854061
Stiffness and hysteresis properties of some prosthetic feet.
van Jaarsveld, H W; Grootenboer, H J; de Vries, J; Koopman, H F
1990-12-01
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
Variable stiffness and damping suspension system for train
NASA Astrophysics Data System (ADS)
Sun, Shuaishuai; Deng, Huaxia; Li, Weihua
2014-03-01
As the vibration of high speed train becomes fierce when the train runs at high speed, it is crucial to develop a novel suspension system to negotiate train's vibration. This paper presents a novel suspension based on Magnetorheological fluid (MRF) damper and MRF based smart air spring. The MRF damper is used to generate variable damping while the smart air spring is used to generate field-dependent stiffness. In this paper, the two kind smart devices, MRF dampers and smart air spring, are developed firstly. Then the dynamic performances of these two devices are tested by MTS. Based on the testing results, the two devices are equipped to a high speed train which is built in ADAMS. The skyhook control algorithm is employed to control the novel suspension. In order to compare the vibration suppression capability of the novel suspension with other kind suspensions, three other different suspension systems are also considered and simulated in this paper. The other three kind suspensions are variable damping with fixed stiffness suspension, variable stiffness with fixed damping suspension and passive suspension. The simulation results indicate that the variable damping and stiffness suspension suppresses the vibration of high speed train better than the other three suspension systems.
INTERIOR VIEW WITH STIFF LEG LADLE CRANE OPERATOR, LUKE WALKER, ...
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
Diabetes and diastolic function: stiffness and relaxation from transmitral flow.
Riordan, Matt M; Chung, Charles S; Kovcs, Sndor J
2005-12-01
To characterize the mechanism by which diabetes affects the heart in diabetic (n = 15) and age-matched control subjects (n = 15), we quantified and compared diastolic function (DF) in terms of chamber stiffness and viscosity/relaxation by analyzing Doppler E- and E'-waves and simultaneous (high-fidelity) hemodynamic data. We compared tau, standard Doppler indexes and indexes of stiffness and viscosity/relaxation computed via the parameterized diastolic filling (PDF) formalism. Three PDF parameters uniquely characterize each E-wave in terms of load (x(o)), viscoelasticity or viscosity/relaxation (c) and stiffness (k). Significant differences for c (p = 0.00004), the peak atrioventricular pressure gradient (kx(o)) (p = 0.02) and the stored elastic energy available for early filling (1/2kx(o)2) (p = 0.04) were found. The only conventional index attaining significance was E-wave acceleration time (p = 0.007). Neither time constant of isovolumic relaxation (tau) nor E-wave deceleration time, E', k or x(o) differentiated between groups. We conclude that PDF based DF assessment differentiates between diabetic and nondiabetic controls better than conventional echo- or cath-based indexes. Our results in humans agree with published results from animal studies. We conclude that diabetes affects the heart via a quantifiable increase in chamber viscoelasticity (c) rather than an increase in chamber stiffness (k) and that phenotypic characterization of diabetic cardiomyopathy is facilitated by DF assessment via the PDF formalism. PMID:16344121
Flexural stiffness of feather shafts: geometry rules over material properties.
Bachmann, Thomas; Emmerlich, Jens; Baumgartner, Werner; Schneider, Jochen M; Wagner, Hermann
2012-02-01
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
Cardiovascular Health and Arterial Stiffness: The Maine Syracuse Longitudinal Study
Crichton, Georgina E; Elias, Merrill F; Robbins, Michael A
2014-01-01
Ideal cardiovascular health is a recently defined construct by the American Heart Association (AHA) to promote cardiovascular disease reduction. Arterial stiffness is a major risk factor for cardiovascular disease. The extent to which the presence of multiple prevalent cardiovascular risk factors and health behaviors is associated with arterial stiffness is unknown. The aim of this study was to examine the association between the AHA construct of cardiovascular health and arterial stiffness, as indexed by pulse wave velocity and pulse pressure. The AHA health metrics, comprising of four health behaviors (smoking, body mass index, physical activity, and diet) and three health factors (total cholesterol, blood pressure, and fasting plasma glucose) were evaluated among 505 participants in the Maine-Syracuse Longitudinal Study. Outcome measures were carotid-femoral pulse wave velocity (PWV) and pulse pressure measured at 4 to 5-year follow-up. Better cardiovascular health, comprising both health factors and behaviors, was associated with lower arterial stiffness, as indexed by pulse wave velocity and pulse pressure. Those with at least five health metrics at ideal levels had significantly lower PWV (9.8 m/s) than those with two or less ideal health metrics (11.7 m/s) (P<0.001). This finding remained with the addition of demographic and PWV-related variables (P=0.004). PMID:24384629
Smart fabric adaptive stiffness for active vibration absorbers
NASA Astrophysics Data System (ADS)
Albanese, Anne-Marie; Cunefare, Kenneth A.
2004-07-01
Unconstrained magnetorheological-elastomers (MRE) experience a stiffness increase and elastomeric deformation in response to an applied magnetic field. An MRE consists of ferromagnetic particles dispersed in a host elastomer matrix. This study considers whether the stiffness change of MRE springs is due to magnetic particle-to-particle interactions or to elastomer deformation. If the stiffening is attributable to magnetic particle interaction, then it should occur even in the absence of the elastomer. To test this hypothesis, a smart fabric consisting of low-carbon steel thread in one direction and nonmagnetic thread in the other was created. Two extension springs were placed in parallel with this smart fabric, and placed in between two iron masses. An electromagnet coil wound about one of the masses provided the source of magnetic field across the smart fabric. The frequency response of the device was measured when the coil was driven by a DC current, at 0.5 Amp increments, from 0 to 4. The device exhibited a 33% increase in stiffness at 4 Amps compared to the stiffness at 0 Amps. While this shift is not as large as shifts observed in MREs, the design was not optimized for iron content, and only had a 0.6% iron content.
Automated Liver Stiffness Measurements with Magnetic Resonance Elastography
Dzyubak, Bogdan; Glaser, Kevin; Yin, Meng; Talwalkar, Jayant; Chen, Jun; Manduca, Armando; Ehman, Richard L.
2012-01-01
Purpose To provide a fully-automated algorithm for obtaining stiffness measurements from hepatic MR Elastography images that are consistent with measurements performed by expert readers. Materials and Methods An initial liver contour was found using an adaptive threshold and expanded using an active contour to select a homogeneous area of the liver. The confidence map generated during the stiffness calculation was used to select a region of reliable wave propagation. The average stiffness within the automatically-generated ROI was compared to measurements by two trained readers in a set of 88 clinical test cases ranging from healthy to severely fibrotic. Results The stiffness measurements reported by the readers differed by ?6.76% 22.8 % (95% confidence) and had an ICC of 0.972 (p<0.05).The algorithm and the more experienced reader differed by 4.32% 14.9 with an ICC of 0.987. Conclusion The automated algorithm performed reliably, even though MRE acquisitions often have motion artifacts present. The correlation between the automated measurements and those from the trained readers was superior to the correlation between the readers. PMID:23281171
Nanostructured conducting polymers for stiffness controlled cell adhesion
NASA Astrophysics Data System (ADS)
Moyen, Eric; Hama, Adel; Ismailova, Esma; Assaud, Loic; Malliaras, George; Hanbücken, Margrit; Owens, Roisin M.
2016-02-01
We propose a facile and reproducible method, based on ultra thin porous alumina membranes, to produce cm2 ordered arrays of nano-pores and nano-pillars on any kind of substrates. In particular our method enables the fabrication of conducting polymers nano-structures, such as poly[3,4-ethylenedioxythiophene]:poly[styrene sulfonate] (PEDOT:PSS). Here, we demonstrate the potential interest of those templates with controlled cell adhesion studies. The triggering of the eventual fate of the cell (proliferation, death, differentiation or migration) is mediated through chemical cues from the adsorbed proteins and physical cues such as surface energy, stiffness and topography. Interestingly, as well as through material properties, stiffness modifications can be induced by nano-topography, the ability of nano-pillars to bend defining an effective stiffness. By controlling the diameter, length, depth and material of the nano-structures, one can possibly tune the effective stiffness of a (nano) structured substrate. First results indicate a possible change in the fate of living cells on such nano-patterned devices, whether they are made of conducting polymer (soft material) or silicon (hard material).
Riparian Sediment Delivery Ratio: Stiff Diagrams and Artifical Neural Networks
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...
Stiffness of hair bundles in the chick cochlea.
Szymko, Y M; Dimitri, P S; Saunders, J C
1992-05-01
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
Stiffness of the gerbil basilar membrane: radial and longitudinal variations.
Emadi, Gulam; Richter, Claus-Peter; Dallos, Peter
2004-01-01
Experimental data on the mechanical properties of the tissues of the mammalian cochlea are essential for understanding the frequency- and location-dependent motion patterns that result in response to incoming sound waves. Within the cochlea, sound-induced vibrations are transduced into neural activity by the organ of Corti, the gross motion of which is dependent on the motion of the underlying basilar membrane. In this study we present data on stiffness of the gerbil basilar membrane measured at multiple positions within a cochlear cross section and at multiple locations along the length of the cochlea. A basic analysis of these data using relatively simple models of cochlear mechanics reveals our most important result: the experimentally measured longitudinal stiffness gradient at the middle of the pectinate zone of the basilar membrane (4.43 dB/mm) can account for changes of best frequency along the length of the cochlea. Furthermore, our results indicate qualitative changes of stiffness-deflection curves as a function of radial position; in particular, there are differences in the rate of stiffness growth with increasing tissue deflection. Longitudinal coupling within the basilar membrane/organ of Corti complex is determined to have a space constant of 21 microm in the middle turn of the cochlea. The bulk of our data was obtained in the hemicochlea preparation, and we include a comparison of this set of data to data obtained in vivo. PMID:14523077
Influence of Passive Stiffness of Hamstrings on Postural Stability
Kuszewski, Michał; Gnat, Rafał; Sobota, Grzegorz; Myśliwiec, Andrzej
2015-01-01
The aim of the study was to explore whether passive stiffness of the hamstrings influences the strategy of maintaining postural stability. A sample of 50 subjects was selected; the final analyses were based on data of 41 individuals (33 men, 8 women) aged 21 to 29 (mean = 23.3, SD = 1.1) years. A quasi- experimental ex post facto design with repeated measures was used. Categories of independent variables were obtained directly prior to the measurement of the dependent variables. In stage one of the study, passive knee extension was measured in the supine position to assess hamstring stiffness. In stage two, the magnitude of postural sway in antero-posterior direction was measured, while varying the body position on a stabilometric platform, both with and without visual control. The margin of safety was used as a measure of postural control. The magnitude of the margin of safety increased significantly between the open-eye and closed-eye trials. However, although we registered a visible tendency for a larger increase of the margin of safety associated with lower levels of passive hamstrings stiffness, no significant differences were found. Therefore, this study demonstrated that hamstring stiffness did not influence the strategy used to maintain postural stability. PMID:25964809
NASA Astrophysics Data System (ADS)
Vest, Todd A.; Darlow, Mark S.
1991-07-01
Analysts of beam-like structures are perennially challenged by complex geometries which are not readily translated into beam element models. The Equivalent Beam Stiffness method, or simply EBS, is presented as an extension to and improvement upon the technique of Thomas and Littlewood in which the effective stiffness diameter profile of a freely suspended rotor was estimated by applying the Euler-Bernoulli beam equation to the measured first lateral bending mode shape. The result was a set of new diameters which replaced those determined from drawings. Based upon the more generally applicable Timoshenko form, the EBS method accounts for transverse inertia and shear deformation effects, the latter requiring an a priori estimate of the equivalent stiffness diameter. Additional improvement is provided by using a continuous description of the mass and inertia properties, rather than the lumped-mass representation used previously, and an analytical approach to the extraction procedure. This allows the bending stiffness to be determined throughout the structure, while other methods to the inverse beam dynamics problem, mostly optimisation-based, determine discrete values. The effects of measurement errors are examined and it is shown the EBS method provides reasonable extractions in the presence of noise levels akin to careful modal test data. The successful application of the technique to two full-scale turbine shafts will be discussed in Part II.
Fransson, A.; Tsang, C.-F.; Rutqvist, J.; Gustafson, G.
2010-05-01
Sealing of tunnels in fractured rocks is commonly performed by pre- or post-excavation grouting. The grouting boreholes are frequently drilled close to the tunnel wall, an area where rock stresses can be low and fractures can more easily open up during grout pressurization. In this paper we suggest that data from hydraulic testing and grouting can be used to identify grout-induced fracture opening, to estimate fracture stiffness of such fractures, and to evaluate its impact on the grout performance. A conceptual model and a method are presented for estimating fracture stiffness. The method is demonstrated using grouting data from four pre-excavation grouting boreholes at a shallow tunnel (50 m) in Nygard, Sweden, and two post-excavation grouting boreholes at a deep tunnel (450 m) in Aespoe HRL, Sweden. The estimated stiffness of intersecting fractures for the boreholes at the shallow Nygard tunnel are low (2-5 GPa/m) and in agreement with literature data from field experiments at other fractured rock sites. Higher stiffness was obtained for the deeper tunnel boreholes at Aespoe which is reasonable considering that generally higher rock stresses are expected at greater depths. Our method of identifying and evaluating the properties and impact of deforming fractures might be most applicable when grouting takes place in boreholes adjacent to the tunnel wall, where local stresses might be low and where deforming (opening) fractures may take most of the grout.
Acute exercise modifies titin phosphorylation and increases cardiac myofilament stiffness
Mller, Anna E.; Kreiner, Matthias; Ktter, Sebastian; Lassak, Philipp; Bloch, Wilhelm; Suhr, Frank; Krger, Martina
2014-01-01
Titin-based myofilament stiffness is largely modulated by phosphorylation of its elastic I-band regions N2-Bus (decreases passive stiffness, PT) and PEVK (increases PT). Here, we tested the hypothesis that acute exercise changes titin phosphorylation and modifies myofilament stiffness. Adult rats were exercised on a treadmill for 15 min, untrained animals served as controls. Titin phosphorylation was determined by Western blot analysis using phosphospecific antibodies to Ser4099 and Ser4010 in the N2-Bus region (PKG and PKA-dependent. respectively), and to Ser11878 and Ser 12022 in the PEVK region (PKC? and CaMKII?-dependent, respectively). Passive tension was determined by step-wise stretching of isolated skinned cardiomyocytes to sarcomere length (SL) ranging from 1.9 to 2.4 ?m and showed a significantly increased PT from exercised samples, compared to controls. In cardiac samples titin N2-Bus phosphorylation was significantly decreased by 40% at Ser4099, however, no significant changes were observed at Ser4010. PEVK phosphorylation at Ser11878 was significantly increased, which is probably mediated by the observed exercise-induced increase in PKC? activity. Interestingly, relative phosphorylation of Ser12022 was substantially decreased in the exercised samples. Surprisingly, in skeletal samples from acutely exercised animals we detected a significant decrease in PEVK phosphorylation at Ser11878 and an increase in Ser12022 phosphorylation; however, PKC? activity remained unchanged. In summary, our data show that a single exercise bout of 15 min affects titin domain phosphorylation and titin-based myocyte stiffness with obviously divergent effects in cardiac and skeletal muscle tissues. The observed changes in titin stiffness could play an important role in adapting the passive and active properties of the myocardium and the skeletal muscle to increased physical activity. PMID:25477822
Vlachov, Jana; Knig, Rebekka; Johannsmann, Diethelm
2015-01-01
The stiffness of micron-sized sphere-plate contacts was studied by employing high frequency, tangential excitation of variable amplitude (0-20 nm). The contacts were established between glass spheres and the surface of a quartz crystal microbalance (QCM), where the resonator surface had been coated with either sputtered SiO2 or a spin-cast layer of poly(methyl methacrylate) (PMMA). The results from experiments undertaken in the dry state and in water are compared. Building on the shifts in the resonance frequency and resonance bandwidth, the instrument determines the real and the imaginary part of the contact stiffness, where the imaginary part quantifies dissipative processes. The method is closely analogous to related procedures in AFM-based metrology. The real part of the contact stiffness as a function of normal load can be fitted with the Johnson-Kendall-Roberts (JKR) model. The contact stiffness was found to increase in the presence of liquid water. This finding is tentatively explained by the rocking motion of the spheres, which couples to a squeeze flow of the water close to the contact. The loss tangent of the contact stiffness is on the order of 0.1, where the energy losses are associated with interfacial processes. At high amplitudes partial slip was found to occur. The apparent contact stiffness at large amplitude depends linearly on the amplitude, as predicted by the Cattaneo-Mindlin model. This finding is remarkable insofar, as the Cattaneo-Mindlin model assumes Coulomb friction inside the sliding region. Coulomb friction is typically viewed as a macroscopic concept, related to surface roughness. An alternative model (formulated by Savkoor), which assumes a constant frictional stress in the sliding zone independent of the normal pressure, is inconsistent with the experimental data. The apparent friction coefficients slightly increase with normal force, which can be explained by nanoroughness. In other words, contact splitting (i.e., a transport of shear stress across many small contacts, rather than a few large ones) can be exploited to reduce partial slip. PMID:25977855
Vlachov, Jana; Knig, Rebekka
2015-01-01
Summary The stiffness of micron-sized sphereplate contacts was studied by employing high frequency, tangential excitation of variable amplitude (020 nm). The contacts were established between glass spheres and the surface of a quartz crystal microbalance (QCM), where the resonator surface had been coated with either sputtered SiO2 or a spin-cast layer of poly(methyl methacrylate) (PMMA). The results from experiments undertaken in the dry state and in water are compared. Building on the shifts in the resonance frequency and resonance bandwidth, the instrument determines the real and the imaginary part of the contact stiffness, where the imaginary part quantifies dissipative processes. The method is closely analogous to related procedures in AFM-based metrology. The real part of the contact stiffness as a function of normal load can be fitted with the JohnsonKendallRoberts (JKR) model. The contact stiffness was found to increase in the presence of liquid water. This finding is tentatively explained by the rocking motion of the spheres, which couples to a squeeze flow of the water close to the contact. The loss tangent of the contact stiffness is on the order of 0.1, where the energy losses are associated with interfacial processes. At high amplitudes partial slip was found to occur. The apparent contact stiffness at large amplitude depends linearly on the amplitude, as predicted by the CattaneoMindlin model. This finding is remarkable insofar, as the CattaneoMindlin model assumes Coulomb friction inside the sliding region. Coulomb friction is typically viewed as a macroscopic concept, related to surface roughness. An alternative model (formulated by Savkoor), which assumes a constant frictional stress in the sliding zone independent of the normal pressure, is inconsistent with the experimental data. The apparent friction coefficients slightly increase with normal force, which can be explained by nanoroughness. In other words, contact splitting (i.e., a transport of shear stress across many small contacts, rather than a few large ones) can be exploited to reduce partial slip. PMID:25977855
On the role of CFRP reinforcement for wood beams stiffness
NASA Astrophysics Data System (ADS)
Ianasi, A. C.
2015-11-01
In recent years, carbon fiber composites have been increasingly used in different ways in reinforcing structural elements. Specifically, the use of composite materials as a reinforcement for wood beams under bending loads requires paying attention to several aspects of the problem such as the number of the composite layers applied on the wood beams. Study consolidation of composites revealed that they are made by bonding fibrous material impregnated with resin on the surface of various elements, to restore or increase the load carrying capacity (bending, cutting, compression or torque) without significant damage of their rigidity. Fibers used in building applications can be fiberglass, aramid or carbon. Items that can be strengthened are concrete, brick, wood, steel and stone, and in terms of structural beams, walls, columns and floors. This paper describes an experimental study which was designed to evaluate the effect of composite material on the stiffness of the wood beams. It proposes a summary of the fundamental principles of analysis of composite materials and the design and use. The type of reinforcement used on the beams is the carbon fiber reinforced polymer (CFRP) sheet and plates and also an epoxy resin for bonding all the elements. Structural epoxy resins remain the primary choice of adhesive to form the bond to fiber-reinforced plastics and are the generally accepted adhesives in bonded CFRP-wood connections. The advantages of using epoxy resin in comparison to common wood-laminating adhesives are their gap-filling qualities and the low clamping pressures that are required to form the bond between carbon fiber plates or sheets and the wood beams. Mechanical tests performed on the reinforced wood beams showed that CFRP materials may produce flexural displacement and lifting increases of the beams. Observations of the experimental load-displacement relationships showed that bending strength increased for wood beams reinforced with CFRP composite plates and sheets compared to those without CFRP reinforcement. The main conclusion of the tests is that the tensioning forces allow beam taking a maximum load for a while, something that is particularly useful when we consider a real construction, so in case of excess lift beam, we have time to take strengthening measures and when is about a catastrophic request (earthquake) the construction remain partially functional. The experiments have shown that the method of increasing resistance of wood constructions with composite materials is good for it. The solution is easy to implement and has low costs.
NASA Technical Reports Server (NTRS)
Kwanka, K.; Ortinger, W.; Steckel, J.
1994-01-01
First experimental investigations performed on a new test rig are presented. For a staggered labyrinth seal with fourteen cavities the stiffness coefficient and the leakage flow are measured. The experimental results are compared to calculated results which are obtained by a one-volume bulk-flow theory. A perturbation analysis is made for seven terms. It is found out that the friction factors have great impact on the dynamic coefficients. They are obtained by turbulent flow computation by a finite-volume model with the Reynolds equations used as basic equations.
Kim, Hyun Seon; Seung, Jaeho; Lee, Ju Hyun; Chung, Byung Ha; Yang, Chul Woo
2015-01-01
Background Arterial stiffness is closely associated with cardiovascular disease (CVD) in end stage renal disease (ESRD) patients. However, the clinical significance of pre-transplant arterial stiffness and the impact of kidney transplantation (KT) on arterial stiffness have not yet been determined. Method We measured the brachial-ankle pulse wave velocity (baPWV) before KT and one year after KT. We evaluated the potential utility of pre-transplant baPWV as a screening test to predict CVD. The impact of KT on progression of arterial stiffness was evaluated according to changes in baPWV after KT. The factors that influence the change of baPWV after KT were also examined. Result The mean value of pre-transplant baPWV was 1508 300 cm/s in ESRD patients; 93.4% had a higher baPWV value than healthy controls. Pre-transplant baPWV was higher in patients with CVD than in those without CVD (1800 440 vs. 1491 265 cm/s, p<0.05), and was a strong predictive factor of CVD (OR 1.003, p<0.05). The optimal cut-off value of baPWV for the detection of CVD was 1591 cm/s, and this value was an independent predictor of CVD in KT recipients (OR 6.3, p<0.05). The post-transplant baPWV was significantly decreased compared to that of pre-transplant rates (1418 235 vs. 1517 293 cm/s, p<0.05), and progression of arterial stiffness was not observed in 86.9% patients. Logistic regression analysis revealed that higher body mass index and the degree of increase in calcium levels were independent risk factors that affected baPWV after KT. Conclusions Evaluation of arterial stiffness with baPWV is a useful screening test for predicting CVD after KT, and KT is effective in preventing the progression of arterial stiffness in ESRD patients. PMID:26406607
Fatigue, Vertical Leg Stiffness, and Stiffness Control Strategies in Males and Females
Padua, Darin A; Arnold, Brent L; Perrin, David H; Gansneder, Bruce M; Carcia, Christopher R; Granata, Kevin P
2006-01-01
Context: Fatigue appears to influence musculoskeletal injury rates during athletic activities, but whether males and females respond differently to fatigue is unknown. Objective: To determine the influence of fatigue on vertical leg stiffness (K VERT) and muscle activation and joint movement strategies and whether healthy males and females respond similarly to fatigue. Design: Repeated-measures design with all data collected during a single laboratory session. Setting: Laboratory. Patients or Other Participants: Physically active males (n = 11) and females (n = 10). Intervention(s): Subjects performed hopping protocols at 2 frequencies before and after fatigue, which was induced by repeated squatting at submaximal loads. Main Outcome Measure(s): We measured K VERT with a forceplate and peak muscle activity of the quadriceps, hamstrings, gastrocnemius, soleus, and anterior tibialis muscles with surface electromyography. Sagittal-plane kinematics at the knee and ankle were recorded with an electrogoniometer. Results: After fatigue, K VERT was unchanged for all subjects. However, both males and females demonstrated reduced peak hamstrings ( P = .002) and anterior tibialis ( P = .001) activation, coupled with increased gastrocnemius ( P = .005) and soleus ( P = .001) peak activity, as well as increased quadriceps-hamstrings ( P = .005) and gastrocnemius/soleus-anterior tibialis coactivation ratios ( P = .03) after fatigue. Overall, females demonstrated greater quadriceps-hamstrings coactivation ratios than males, regardless of the fatigue condition ( P = .026). Only females showed increased knee flexion at initial contact after fatigue during hopping ( P = .03). Conclusions: Although K VERT was unaffected, the peak muscle activation and joint movement strategies used to modulate K VERT were affected after fatigue. Once fatigued, both males and females used an ankle-dominant strategy, with greater reliance on the ankle musculature and less on the knee musculature. Also, once fatigued, all subjects used an antagonist inhibition strategy by minimizing antagonist coactivation. Overall, females used a more quadriceps-dominant strategy than males, showing greater quadriceps activity and a larger quadriceps-hamstrings coactivation ratio. Changes in muscle activation and coactivation ratios because of fatigue and sex are suggested to alter knee joint stability and increase anterior cruciate ligament injury risk. PMID:17043698
Diffusion Coefficients in White Dwarfs
NASA Astrophysics Data System (ADS)
Saumon, D.; Starrett, C. E.; Daligault, J.
2015-06-01
Models of diffusion in white dwarfs universally rely on the coefficients calculated by Paquette et al. (1986). We present new calculations of diffusion coefficients based on an advanced microscopic theory of dense plasmas and a numerical simulation approach that intrinsically accounts for multiple collisions. Our method is validated against a state-of-the-art method and we present results for the diffusion of carbon ions in a helium plasma.
Wrong Signs in Regression Coefficients
NASA Technical Reports Server (NTRS)
McGee, Holly
1999-01-01
When using parametric cost estimation, it is important to note the possibility of the regression coefficients having the wrong sign. A wrong sign is defined as a sign on the regression coefficient opposite to the researcher's intuition and experience. Some possible causes for the wrong sign discussed in this paper are a small range of x's, leverage points, missing variables, multicollinearity, and computational error. Additionally, techniques for determining the cause of the wrong sign are given.
NASA Technical Reports Server (NTRS)
Childs, Dara W.; Elrod, David; Hale, Keith
1989-01-01
Test results are presented for leakage and rotordynamic coefficients for seven honeycomb seals. All seals have the same radius, length, and clearance; however, the cell depths and diameters are varied. Rotordynamic data, which are presented, consist of the direct and cross-coupled stiffness coefficients and the direct damping coefficients. The rotordynamic-coefficient data show a considerable sensitivity to changes in cell dimensions; however, no clear trends are identifiable. Comparisons of test data for the honeycomb seals with labyrinth and smooth annular seals show the honeycomb seal had the best sealing (minimum leakage) performance, followed in order by the labyrinth and smooth seals. For prerotated fluid entering the seal, in the direction of shaft rotation, the honeycomb seal has the best rotordynamic stability followed in order by the labyrinth and smooth. For no prerotation, or fluid prerotation against shaft rotation, the labyrinth seal has the best rotordynamic stability followed in order by the smooth and honeycomb seals.
NASA Technical Reports Server (NTRS)
Childs, D.; Elrod, D.; Hale, K.
1989-01-01
Test results are presented for leakage and rotordynamic coefficients for seven honeycomb seals. All seals have the same radius, length, and clearance; however, the cell depths and diameters are varied. Rotordynamic data, which are presented, consist of the direct and cross-coupled stiffness coefficients and the direct damping coefficients. The rotordynamic-coefficient data show a considerable sensitivity to changes in cell dimensions; however, no clear trends are identifiable. Comparisons of test data for the honeycomb seals with labyrinth and smooth annular seals shows the honeycomb seal had the best sealing (minimum leakage) performance, followed in order by the labyrinth and smooth seals. For prerotated fluids entering the seal, in the direction of shaft rotation, the honeycomb seal has the best rotordynamic stability followed in order by the labyrinth and smooth. For no prerotation, or fluid prerotation against shaft rotation, the labyrinth seal has the best rotordynamic stability followed in order by the smooth and honeycomb seals.
Zero finite-temperature charge stiffness within the half-filled 1D Hubbard model
Carmelo, J.M.P.; Beijing Computational Science Research Center, Beijing 100084; Institut fr Theoretische Physik III, Universitt Stuttgart, D-70550 Stuttgart ; Gu, Shi-Jian; Department of Physics and ITP, Chinese University of Hong Kong, Hong Kong ; Sacramento, P.D.; Beijing Computational Science Research Center, Beijing 100084
2013-12-15
Even though the one-dimensional (1D) Hubbard model is solvable by the Bethe ansatz, at half-filling its finite-temperature T>0 transport properties remain poorly understood. In this paper we combine that solution with symmetry to show that within that prominent T=0 1D insulator the charge stiffness D(T) vanishes for T>0 and finite values of the on-site repulsion U in the thermodynamic limit. This result is exact and clarifies a long-standing open problem. It rules out that at half-filling the model is an ideal conductor in the thermodynamic limit. Whether at finite T and U>0 it is an ideal insulator or a normal resistor remains an open question. That at half-filling the charge stiffness is finite at U=0 and vanishes for U>0 is found to result from a general transition from a conductor to an insulator or resistor occurring at U=U{sub c}=0 for all finite temperatures T>0. (At T=0 such a transition is the quantum metal to MottHubbard-insulator transition.) The interplay of the ?-spin SU(2) symmetry with the hidden U(1) symmetry beyond SO(4) is found to play a central role in the unusual finite-temperature charge transport properties of the 1D half-filled Hubbard model. -- Highlights: The charge stiffness of the half-filled 1D Hubbard model is evaluated. Its value is controlled by the model symmetry operator algebras. We find that there is no charge ballistic transport at finite temperatures T>0. The hidden U(1) symmetry controls the U=0 phase transition for T>0.
Converting Sabine absorption coefficients to random incidence absorption coefficients.
Jeong, Cheol-Ho
2013-06-01
Absorption coefficients measured by the chamber method are referred to as Sabine absorption coefficients, which sometimes exceed unity due to the finite size of a sample and non-uniform intensity in the reverberation chambers under test. In this study, conversion methods from Sabine absorption coefficients to random incidence absorption coefficients are proposed. The overestimations of the Sabine absorption coefficient are investigated theoretically based on Miki's model for porous absorbers backed by a rigid wall or an air cavity, resulting in conversion factors. Additionally, three optimizations are suggested: An optimization method for the surface impedances for locally reacting absorbers, the flow resistivity for extendedly reacting absorbers, and the flow resistance for fabrics. With four porous type absorbers, the conversion methods are validated. For absorbers backed by a rigid wall, the surface impedance optimization produces the best results, while the flow resistivity optimization also yields reasonable results. The flow resistivity and flow resistance optimization for extendedly reacting absorbers are also found to be successful. However, the theoretical conversion factors based on Miki's model do not guarantee reliable estimations, particularly at frequencies below 250 Hz and beyond 2500?Hz. PMID:23742349
Ultrasonographic vascular mechanics to assess arterial stiffness: a review.
Teixeira, Rogério; Vieira, Maria João; Gonçalves, Alexandra; Cardim, Nuno; Gonçalves, Lino
2016-03-01
In recent years, the role of arterial stiffness in the development of cardiovascular diseases has been explored more extensively. Local arterial stiffness may be gauged via ultrasound, measuring pulse transit time relative to changing vessel diameters and distending pressures. Recently, direct vessel-wall tracking systems have been devised based on new ultrasonographic methodologies, such as tissue Doppler imaging and speckle-tracking analysis-vascular mechanics. These advances have been evaluated in varying arterial distributions, are proved surrogates of pulse wave velocity, and are ascending in clinical importance. In the course of this review, we describe fundamental concepts and methodologies involved in ultrasound assessment of vascular mechanics. We also present relevant clinical studies and discuss the potential clinical utility of such diagnostic pursuits. PMID:26546802
Stiff filamentous virus translocations through solid-state nanopores.
McMullen, Angus; de Haan, Hendrick W; Tang, Jay X; Stein, Derek
2014-01-01
The ionic conductance through a nanometer-sized pore in a membrane changes when a biopolymer slides through it, making nanopores sensitive to single molecules in solution. Their possible use for sequencing has motivated numerous studies on how DNA, a semi-flexible polymer, translocates nanopores. Here we study voltage-driven dynamics of the stiff filamentous virus fd with experiments and simulations to investigate the basic physics of polymer translocations. We find that the electric field distribution aligns an approaching fd with the nanopore, promoting its capture, but it also pulls fd sideways against the membrane after failed translocation attempts until thermal fluctuations reorient the virus for translocation. fd is too stiff to translocate in folded configurations. It therefore translocates linearly, exhibiting a voltage-independent mobility and obeying first-passage-time statistics. Surprisingly, lengthwise Brownian motion only partially accounts for the translocation velocity fluctuations. We also observe a voltage-dependent contribution whose origin is only partially determined. PMID:24932700
Vibration in Planetary Gear Systems with Unequal Planet Stiffnesses
NASA Technical Reports Server (NTRS)
Frater, J. L.; August, R.; Oswald, F. B.
1982-01-01
An algorithm suitable for a minicomputer was developed for finding the natural frequencies and mode shapes of a planetary gear system which has unequal stiffnesses between the Sun/planet and planet/ring gear meshes. Mode shapes are represented in the form of graphical computer output that illustrates the lateral and rotational motion of the three coaxial gears and the planet gears. This procedure permits the analysis of gear trains utilizing nonuniform mesh conditions and user specified masses, stiffnesses, and boundary conditions. Numerical integration of the equations of motion for planetary gear systems indicates that this algorithm offers an efficient means of predicting operating speeds which may result in high dynamic tooth loads.
Strong, tough and stiff bioinspired ceramics from brittle constituents
NASA Astrophysics Data System (ADS)
Bouville, Florian; Maire, Eric; Meille, Sylvain; van de Moortèle, Bertrand; Stevenson, Adam J.; Deville, Sylvain
2014-05-01
High strength and high toughness are usually mutually exclusive in engineering materials. In ceramics, improving toughness usually relies on the introduction of a metallic or polymeric ductile phase, but this decreases the material’s strength and stiffness as well as its high-temperature stability. Although natural materials that are both strong and tough rely on a combination of mechanisms operating at different length scales, the relevant structures have been extremely difficult to replicate. Here, we report a bioinspired approach based on widespread ceramic processing techniques for the fabrication of bulk ceramics without a ductile phase and with a unique combination of high strength (470 MPa), high toughness (22 MPa m1/2), and high stiffness (290 GPa). Because only mineral constituents are needed, these ceramics retain their mechanical properties at high temperatures (600 °C). Our bioinspired, material-independent approach should find uses in the design and processing of materials for structural, transportation and energy-related applications.
Stiffness and damping characteristics of aluminum in creep
NASA Technical Reports Server (NTRS)
Berkovits, A.
1977-01-01
Tensile creep tests conducted at 200 C were performed on annealed commercially pure aluminum specimens in order to measure the dominant elevated temperature dislocation processes. Testing consisted of applying small lateral loads to measure flexural stiffness, and vibrating the specimens laterally in order to measure dynamic modulus and internal damping. It was concluded that (1) the strain hardening increased static stiffness and decreased internal damping during early creep, and (2) the dynamic modulus remained essentially constant at the elastic value during creep. These results imply that primary creep may constitute a mechanism of recovery of dislocatory disorder induced by yielding the material during loading, and that the inelastic modulus utilized as a mathematical concept in several creep buckling theories is not a directly measurable material property.
Force, Torque and Stiffness: Interactions in Perceptual Discrimination
Wu, Bing; Klatzky, Roberta L.; Hollis, Ralph L.
2011-01-01
Three experiments investigated whether force and torque cues interact in haptic discrimination of force, torque and stiffness, and if so, how. The statistical relation between force and torque was manipulated across four experimental conditions: Either one type of cue varied while the other was constant, or both varied so as to be positively correlated, negatively correlated, or uncorrelated. Experiment 1 showed that the subjects’ ability to discriminate force was improved by positively correlated torque but impaired with uncorrelated torque, as compared to the constant torque condition. Corresponding effects were found in Experiment 2 for the influence of force on torque discrimination. These findings indicate that force and torque are integrated in perception, rather than being processed as separate dimensions. A further experiment demonstrated facilitation of stiffness discrimination by correlated force and torque, whether the correlation was positive or negative. The findings suggest new means of augmenting haptic feedback to facilitate perception of the properties of soft objects. PMID:21359137
Stabilized multilevel Monte Carlo method for stiff stochastic differential equations
Abdulle, Assyr Blumenthal, Adrian
2013-10-15
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.
A new strategy for stiffness evaluation of sheet metal parts
NASA Astrophysics Data System (ADS)
Cai, Q.; Volk, W.; Dster, A.; Rank, E.
2011-08-01
In the automotive industry, surfaces of styling models are shaped very often in physical models. For example, in the styling process of a car body important design work is realized by clay models and the resulting geometry information typically comes from optical scans. The scanned data is given in the form of point clouds which is then utilized in the virtual planning process for engineering work, e.g. to evaluate the load-carrying capacity. This is an important measure for the stiffness of the car body panels. In this contribution, the following two issues are discussed: what is the suitable geometric representation of the stiffness of the car body and how it is computed if only discrete point clouds exist. In the first part, the suitable geometric representation is identified by constructing continuous CAD models with different geometric parameters, e.g. Gaussian curvature and mean curvature. The stiffness of models is then computed in LS-DYNA and the influence of different geometric parameters is presented based on the simulation result. In the second part, the point clouds from scanned data, rather than continuous CAD models, are directly utilized to estimate the Gaussian curvature, which is normally derived from continuous surfaces. The discrete Gauss-Bonnet algorithm is applied to estimate the Gaussian curvature of the point clouds and the sensitivity of the algorithm with respect to the mesh quality is analyzed. In this way, the stiffness evaluation process in an early stage can be accelerated since the transformation from discrete data to continuous CAD data is labor-intensive. The discrete Gauss-Bonnet algorithm is finally applied to a sheet metal model of the BMW 3 series.
Compact, Stiff, Remotely-Actuable Quick-Release Clamp
NASA Technical Reports Server (NTRS)
Tsai, Ted W. (Inventor)
2000-01-01
The present invention provides a clamp that is compact and lightweight, yet provides high holding strength and stiffness or rigidity. The clamp uses a unique double slant interface design which provides mechanical advantages to resist forces applied to the clamp member as the load increases. The clamp allows for rapid and remote-activated release of the clamp jaws by applying only a small operating force to an over-center lock/release mechanism, such as by pulling a manual tether.
Iron Stores, Hepcidin, and Aortic Stiffness in Individuals with Hypertension
Valenti, Luca; Maloberti, Alessandro; Signorini, Stefano; Milano, Marta; Cesana, Francesca; Cappellini, Fabrizio; Dongiovanni, Paola; Porzio, Marianna; Soriano, Francesco; Brambilla, Maura; Cesana, Giancarlo; Brambilla, Paolo
2015-01-01
Background & Aims Iron accumulation within the arterial wall has been hypothesized to promote atherosclerosis progression. Aim of this study was to evaluate whether the hormone hepcidin and iron stores are associated with arterial stiffness in subjects with essential hypertension. Methods Circulating hepcidin, ferritin, and mutations in the hemochromatosis gene were compared between subjects included in the first vs. third tertile (n=284 each) of carotid-femoral pulse wave velocity (PWV) in an unselected cohort of patients with arterial hypertension. Results At univariate logistic regression analysis, high PWV was associated with higher ferritin levels (p=0.010), but lower hepcidin (p=0.045), and hepcidin ferritin/ratio (p<0.001). Hemochromatosis mutations predisposing to iron overload were associated with high PWV (p=0.025). At multivariate logistic regression analysis, high aortic stiffness was associated with older age, male sex, lower BMI, higher systolic blood pressure and heart rate, hyperferritinemia (OR 2.05, 95% c.i. 1.11-3.17 per log ng/ml; p=0.022), and lower circulating hepcidin concentration (OR 0.29, 95% c.i. 0.16-0.51 per log ng/ml; p<0.001). In subgroup analyses, high PWV was associated with indices of target organ damage, including micro-albuminuria (n=125, p=0.038), lower ejection fraction (n=175, p=0.031), cardiac diastolic dysfunction (p=0.004), and lower S wave peak systolic velocity (p<0.001). Ferritin was associated with cardiac diastolic dysfunction, independently of confounders (p=0.006). Conclusions In conclusion, hyperferritinemia is associated with high aortic stiffness and cardiac diastolic dysfunction, while low circulating hepcidin with high aortic stiffness. PMID:26244503
Stiffness Study of Wound-Filament Pressure Vessels
NASA Technical Reports Server (NTRS)
Verderaime, V.
1986-01-01
Report presents theoretical and experimental study of stiffness of lightweight, jointed pressure vessels made of wound graphite fibers and epoxy. Specimens fabricated from layers of graphite fibers, wet with epoxy, on aluminum mandrel. Segment ends thickened with interspersed layers of axially oriented fibers to reduce pinhole bearing stresses and local deformations. Segments cured at 390 degrees F (199 degrees C). Report presents results of vibrational tests of one-quarter-scale models of wound-filament pressure vessels.
Magnetic bearing stiffness control using frequency band filtering
NASA Technical Reports Server (NTRS)
Chen, H. Ming
1989-01-01
Active magnetic bearings can be implemented with frequency band-reject filtering that decreases the bearing stiffness and damping at a small bandwidth around a chosen frequency. The control scheme was used for reducing a rotor dynamic force, such as an imbalance force, transmitted to the bearing stator. The scheme creates additional system vibration modes at the same frequency. It also shows that the amount of force reduction is limited by the stability requirement of these modes.
Development of a variable stiffness spring for adaptive vibration isolators
NASA Astrophysics Data System (ADS)
Cronje, Johan M.; Heyns, P. S.; Theron, Nico J.; Loveday, Philip W.
2004-07-01
Variable stiffness springs allow vibration absorbers and isolators to adapt to changing operating conditions. This paper describes the development of such a spring. The spring was a compound leaf spring and variable stiffness was achieved by separating the two leaf springs using a wax actuator. In the selected design, each spring consisted of an outer (220mm in diameter) and an inner ring connected by three radial beams. A paraffin wax actuator was chosen to affect the separation of the leaf springs. This actuator consisted of a small copper cup containing paraffin wax. When the wax is heated, it changes from a solid to a liquid with an associated volume change that is used to drive an output shaft. A hot-air gun was used to heat and cool the wax actuator. It was found that the wax actuator could produce an 8mm separation of the springs, which increased the stiffness of the spring by 2.7 times, exceeding the typical requirement for adaptive absorbers and isolators. The loss factor, of the variable stiffness spring, was less than 0.12. The measured response times for the open-loop system were 82s and 109s for heating and cooling respectively. A linear sliding potentiometer was used to measure the spring separation and proportional and derivative feedback control was used to control the current supplied to the heating element thus reducing the response time to less than 30s for small step changes. Further improvement in response time could be achieved by more directly heating and cooling of the paraffin wax in the actuator.
Biomechanical imaging of cell stiffness and prestress with subcellular resolution.
Canovi?, Elizabeth P; Seidl, D Thomas; Polio, Samuel R; Oberai, Assad A; Barbone, Paul E; Stamenovi?, Dimitrije; Smith, Michael L
2014-06-01
Knowledge of cell mechanical properties, such as elastic modulus, is essential to understanding the mechanisms by which cells carry out many integrated functions in health and disease. Cellular stiffness is regulated by the composition, structural organization, and indigenous mechanical stress (or prestress) borne by the cytoskeleton. Current methods for measuring stiffness and cytoskeletal prestress of living cells necessitate either limited spatial resolution but with high speed, or spatial maps of the entire cell at the expense of long imaging times. We have developed a novel technique, called biomechanical imaging, for generating maps of both cellular stiffness and prestress that requires less than 30 s of interrogation time, but which provides subcellular spatial resolution. The technique is based on the ability to measure tractions applied to the cell while simultaneously observing cell deformation, combined with capability to solve an elastic inverse problem to find cell stiffness and prestress distributions. We demonstrated the application of this technique by carrying out detailed mapping of the shear modulus and cytoskeletal prestress distributions of 3T3 fibroblasts, making no assumptions regarding those distributions or the correlation between them. We also showed that on the whole cell level, the average shear modulus is closely associated with the average prestress, which is consistent with the data from the literature. Data collection is a straightforward procedure that lends itself to other biochemical/biomechanical interventions. Biomechanical imaging thus offers a new tool that can be used in studies of cell biomechanics and mechanobiology where fast imaging of cell properties and prestress is desired at subcellular resolution. PMID:24022327
Cardiomyocyte subdomain contractility arising from microenvironmental stiffness and topography.
Broughton, Kathleen M; Russell, Brenda
2015-06-01
Cellular structure and function are interdependent. To understand this relationship in beating heart cells, individual neonatal rat ventricular myocytes (NRVMs) were analyzed one and 3days after plating when cultured on different stiffness (100, 400kPa) and surface structures (flat or [Formula: see text] high, [Formula: see text] diameter, microposts spaced [Formula: see text] apart) manufactured from polydimethylsiloxane. Myofibril structure seen by immunohistochemistry was organized in three dimensions when NRVMs were attached to microposts. On day three, paxillin distribution near the post serving as cellular anchorage was quantified on both soft posts (12.04% of total voxel count) and stiff posts (8.16%). Living NRVMs were analyzed using line scans for sarcomeric shortening and shortening velocity, and traction force microscopy for surface stress and surface tension. One day after plating, NRVMs shortened more on soft posts ([Formula: see text] at [Formula: see text]) compared to either soft flat ([Formula: see text] at [Formula: see text]), stiff posts ([Formula: see text] at [Formula: see text]) or stiff flat ([Formula: see text] at [Formula: see text]). NRVMs have decreased shortening and shortening velocity on soft posts ([Formula: see text] at [Formula: see text]) compared to soft flat ([Formula: see text] at [Formula: see text]) substrates. The surface stress and surface tension increased over time for both soft post ([Formula: see text] and [Formula: see text] to [Formula: see text] and [Formula: see text]) and flat ([Formula: see text] and [Formula: see text] to [Formula: see text] and [Formula: see text]) substrates. Paxillin displacement during contraction on day three was significantly greater in NRVMs attached to soft posts [Formula: see text] compared to flat [Formula: see text] substrates. The volume and time creating four-dimensional data, interpreted by structural engineering theory, demonstrate subdomain structure is maintained by the counterbalance between the external load acting upon and the internal forces generated by the cardiomyocyte. These findings provide further insight into localized regulation of cellular mechanical function. PMID:25273278
Arterial stiffness and cardiovascular events: The Framingham Heart Study
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
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. PMID:20083680
Passive stiffness of rat skeletal muscle undernourished during fetal development
Toscano, Ana Elisa; Ferraz, Karla Mnica; de Castro, Raul Manhes; Canon, Francis
2010-01-01
OBJECTIVES: The aim of the study was to investigate the effect of fetal undernutrition on the passive mechanical properties of skeletal muscle of weaned and young adult rats. INTRODUCTION: A poor nutrition supply during fetal development affects physiological functions of the fetus. From a mechanical point of view, skeletal muscle can be also characterized by its resistance to passive stretch. METHODS: Male Wistar rats were divided into two groups according to their mother's diet during pregnancy: a control group (mothers fed a 17% protein diet) and an isocaloric low?protein group (mothers fed a 7.8% protein diet). At birth, all mothers received a standardized meal ad libitum. At the age of 25 and 90days, the soleus muscle and extensor digitorum longus (EDL) muscles were removed in order to test the passive mechanical properties. A first mechanical test consisted of an incremental stepwise extension test using fast velocity stretching (500mm/s) enabling us to measure, for each extension stepwise, the dynamic stress (?d) and the steady stress (?s). A second test consisted of a slow velocity stretch in order to calculate normalized stiffness and tangent modulus from the stressstrain relationship. RESULTS: The results for the mechanical properties showed an important increase in passive stiffness in both the soleus and EDL muscles in weaned rat. In contrast, no modification was observed in young adult rats. CONCLUSIONS: The increase in passive stiffness in skeletal muscle of weaned rat submitted to intrauterine undernutrition it is most likely due to changes in muscle passive stiffness. PMID:21340228
Arterial Stiffness in Patients with Deep and Lobar Intracerebral Hemorrhage
Guideri, Francesca; Di Donato, Ilaria; Tassi, Rossana; Marotta, Giovanna; Lo Giudice, Giuseppe; D'Andrea, Paolo; Martini, Giuseppe
2014-01-01
Background and Purpose Intracerebral hemorrhage (ICH) accounts for approximately 10% of stroke cases. Hypertension may play a role in the pathogenesis of ICH that occurs in the basal ganglia, thalamus, pons, and cerebellum, but not in that of lobar ICH. Hypertension contributes to decreased elasticity of arteries, thereby increasing the likelihood of rupture in response to acute elevation in intravascular pressure. This study aimed to evaluate arterial stiffness (using the arterial stiffness index [ASI]) in patients with deep (putaminal and thalamic) ICH in comparison with patients with lobar ICH. Methods We enrolled 64 patients (meanSD age: 69.310.7 years; 47 men and 17 women) among 73 who referred consecutively to our department for intraparenchymal hemorrhage and underwent brain computed tomography (CT) and cerebral angio-CT. In all the subjects, 24-hour heart rates and blood pressures were monitored. The linear regression slope of diastolic on systolic blood pressure was assumed as a global measure of arterial compliance, and its complement (1 minus the slope), ASI, has been considered as a measure of arterial stiffness. Results In the patients with deep ICH, ASI was significantly higher than in the patients with lobar ICH (0.640.19 vs. 0.530.17, P=0.04). Conclusions Our results suggest that in deep ICH, arterial stiffening represents a possible pathogenetic factor that modifies arterial wall properties and contributes to vascular rupture in response to intravascular pressure acute elevation. Therapeutic strategies that reduce arterial stiffness may potentially lower the incidence of deep hemorrhagic stroke. PMID:25328877
Human corneal epithelial cell response to substrate stiffness.
Molladavoodi, Sara; Kwon, Hyock-Ju; Medley, John; Gorbet, Maud
2015-01-01
It has been reported that mechanical stimulus can affect cellular behavior. While induced differentiation in stem cells and proliferation and directional migration in fibroblasts are reported as responses to mechanical stimuli, little is known about the response of cells from the cornea. In the present study, we investigated whether changes in substrate stiffness (measured by elastic modulus) affected the behavior of human corneal epithelial cells (HCECs). Polyacrylamide substrates with different elastic moduli (compliant, medium and stiff) were prepared and HCECs were cultured on them. HCECs responses, including cell viability, apoptosis, intercellular adhesion molecule-1 (ICAM-1) expression, integrin-?3?1 expression and changes in cytoskeleton structure (actin fibers) and migratory behavior, were studied. No statistically significant cell activation, as measured by ICAM-1 expression, was observed. However, on compliant substrates, a higher number of cells were found to be apoptotic and disrupted actin fibers were observed. Furthermore, cells displayed a statistically significant lower migration speed on compliant substrates when compared with the stiffer substrates. Thus, corneal epithelial cells respond to changes in substrate stiffness, which may have implications in the understanding and perhaps treatment of corneal diseases, such as keratoconus. PMID:25305512
Origami tubes assembled into stiff, yet reconfigurable structures and metamaterials.
Filipov, Evgueni T; Tachi, Tomohiro; Paulino, Glaucio H
2015-10-01
Thin sheets have long been known to experience an increase in stiffness when they are bent, buckled, or assembled into smaller interlocking structures. We introduce a unique orientation for coupling rigidly foldable origami tubes in a "zipper" fashion that substantially increases the system stiffness and permits only one flexible deformation mode through which the structure can deploy. The flexible deployment of the tubular structures is permitted by localized bending of the origami along prescribed fold lines. All other deformation modes, such as global bending and twisting of the structural system, are substantially stiffer because the tubular assemblages are overconstrained and the thin sheets become engaged in tension and compression. The zipper-coupled tubes yield an unusually large eigenvalue bandgap that represents the unique difference in stiffness between deformation modes. Furthermore, we couple compatible origami tubes into a variety of cellular assemblages that can enhance mechanical characteristics and geometric versatility, leading to a potential design paradigm for structures and metamaterials that can be deployed, stiffened, and tuned. The enhanced mechanical properties, versatility, and adaptivity of these thin sheet systems can provide practical solutions of varying geometric scales in science and engineering. PMID:26351693
Arterial Stiffness and Wave Reflection: Biomarkers of Cardiovascular Risk
Mitchell, Gary F.
2009-01-01
Arterial stiffness and excessive pressure pulsatility have emerged as important risk factors for cardiovascular disease. Arterial stiffness increases with age and in the presence of traditional cardiovascular disease risk factors, such as hypertension, diabetes and lipid disorders. Pathologic stiffening of large arteries with advancing age and risk factor exposure predominantly involves the elastic aorta and carotid arteries, whereas stiffness changes are relatively limited in muscular arteries. Aortic stiffening is associated with increased pulse wave velocity and pulse pressure, which are related but distinct measures of the pulsatile energy content of the pressure waveform. A dramatic increase in pulsatile energy content of pressure and flow waves in the arterial system places considerable pulsatile stress on the heart, large arteries and distal circulation. Large artery stiffening is associated with abnormalities in microvascular structure and function that may contribute to tissue damage, particularly in susceptible high flow organs such as the brain and kidneys. This brief review summarizes results of recent research on risk factors for and adverse effects of large artery stiffening. PMID:20161241
Strength and stiffness reduction factors for infilled frames with openings
NASA Astrophysics Data System (ADS)
Decanini, Luis D.; Liberatore, Laura; Mollaioli, Fabrizio
2014-09-01
Framed structures are usually infilled with masonry walls. They may cause a significant increase in both stiffness and strength, reducing the deformation demand and increasing the energy dissipation capacity of the system. On the other hand, irregular arrangements of the masonry panels may lead to the concentration of damage in some regions, with negative effects; for example soft story mechanisms and shear failures in short columns. Therefore, the presence of infill walls should not be neglected, especially in regions of moderate and high seismicity. To this aim, simple models are available for solid infills walls, such as the diagonal no-tension strut model, while infilled frames with openings have not been adequately investigated. In this study, the effect of openings on the strength and stiffness of infilled frames is investigated by means of about 150 experimental and numerical tests. The main parameters involved are identified and a simple model to take into account the openings in the infills is developed and compared with other models proposed by different researchers. The model, which is based on the use of strength and stiffness reduction factors, takes into account the opening dimensions and presence of reinforcing elements around the opening. An example of an application of the proposed reduction factors is also presented.
Ultrasonic guided interface waves at a soft-stiff boundary.
Bostron, Jason H; Rose, Joseph L; Moose, Clark A
2013-12-01
Interface waves traveling along the boundary between two solids have been studied for nearly a century. However, little attention has been given to the case where interface waves travel at the boundary between a soft and stiff solid and when the soft material is relatively light and viscoelastic. In this paper, the characteristics of interface waves that propagate along a soft-stiff boundary are described. These waves are similar to a leaky Rayleigh-like wave on the stiff solid in terms of the wave velocity and displacement wave structure. Analytical and finite element models are used to model and simulate wave propagation. An example problem of bond evaluation for coatings on metal structures is considered. Experiments on 2.5 cm thick steel plate with 2.5 cm viscoelastic coatings show good agreement to models. Additionally, the results of models and experiments show several promising features that may be used to evaluate bonds in a non-destructive evaluation approach. PMID:25669246
Explicit Integration of Extremely Stiff Reaction Networks: Asymptotic Methods
Guidry, Mike W; Budiardja, R.; Feger, E.; Billings, J. J.; Hix, William Raphael; Messer, O.E.B.; Roche, K. J.; McMahon, E.; He, M.
2013-01-01
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.
Active stiffness modulation of fins using macro fiber composites
NASA Astrophysics Data System (ADS)
Kancharala, Ashok K.; Philen, Michael K.
2013-04-01
Studies on the role of body flexibility in propulsion suggest that fish have the ability to control or modulate the stiffness of the fin for optimized propulsive performance. Fins with certain stiffness might be efficient for a particular set of operating parameters but may be inefficient for other parameters. Therefore active stiffness modulation of a fin can improve the propulsive performance for a range of operating conditions. This paper discusses the preliminary experimental work on the open loop active deformation control of heaving flexible fins using Macro Fiber Composites (MFCs). The effect of important parameters such as oscillation frequency, flexibility of the fin, applied voltage and the phase difference between applied voltage and heaving on propulsive performance are studied and reported. The results indicate that propulsive performance can be improved by active control of the fins. The mean thrust improved by 30- 38% for the fins used in the experiments. The phase difference of ~90 is found to be optimal for maximized propulsive performance for the parameters considered in the study. Furthermore, there exists an optimal voltage magnitude at which the propulsive performance is a maximum for the range of operating conditions.
Helical growth trajectories in plant roots interacting with stiff barriers
NASA Astrophysics Data System (ADS)
Gerbode, Sharon; Noar, Roslyn; Harrison, Maria
2009-03-01
Plant roots successfully navigate heterogeneous soil environments with varying nutrient and water concentrations, as well as a variety of stiff obstacles. While it is thought that the ability of roots to penetrate into a stiff lower soil layer is important for soil erosion, little is known about how a root actually responds to a rigid interface. We have developed a laser sheet imaging technique for recording the 3D growth dynamics of plant roots interacting with stiff barriers. We find that a root encountering an angled interface does not grow in a straight line along the surface, but instead follows a helical trajectory. These experiments build on the pioneering studies of roots grown on a tilted 2D surface, which reported ``root waving,'' a similar curved pattern thought to be caused by the root's sensitivity to both gravity and the rigid surface on which it is grown. Our measurements extend these results to the more physiologically relevant case of 3D growth, where the spiral trajectory can be altered by tuning the relative strengths of the gravity and touch stimuli, providing some intuition for the physical mechanism driving it.
Arterial Stiffness, Oxidative Stress, and Smoke Exposure in Wildland Firefighters
Gaughan, Denise M.; Siegel, Paul D.; Hughes, Michael D.; Chang, Chiung-Yu; Law, Brandon F.; Campbell, Corey R.; Richards, Jennifer C.; Kales, Stefanos F.; Chertok, Marcia; Kobzik, Lester; Nguyen, Phuongson; ODonnell, Carl R.; Kiefer, Max; Wagner, Gregory R.; Christiani, David C.
2015-01-01
Objectives To assess the association between exposure, oxidative stress, symptoms, and cardiorespiratory function in wildland firefighters. Methods We studied two Interagency Hotshot Crews with questionnaires, pulse wave analysis for arterial stiffness, spirometry, urinary 8-iso-prostaglandin F2? (8-isoprostane) and 8-hydroxy-2?-deoxyguanosine (8-OHdG), and the smoke exposure marker (urinary levoglucosan). Arterial stiffness was assessed by examining levels of the aortic augmentation index, expressed as a percentage. An oxidative stress score comprising the average of z-scores created for 8-OHdG and 8-isoprostane was calculated. Results Mean augmentation index % was higher for participants with higher oxidative stress scores after adjusting for smoking status. Specifically for every one unit increase in oxidative stress score the augmentation index % increased 10.5% (95% CI: 2.5, 18.5%). Higher mean lower respiratory symptom score was associated with lower percent predicted forced expiratory volume in one second/forced vital capacity. Conclusions Biomarkers of oxidative stress may serve as indicators of arterial stiffness in wildland firefighters. PMID:24909863
Normalized stiffness ratios for mechanical characterization of isotropic acoustic foams.
Sahraoui, Sohbi; Brouard, Bruno; Benyahia, Lazhar; Parmentier, Damien; Geslain, Alan
2013-12-01
This paper presents a method for the mechanical characterization of isotropic foams at low frequency. The objective of this study is to determine the Young's modulus, the Poisson's ratio, and the loss factor of commercially available foam plates. The method is applied on porous samples having square and circular sections. The main idea of this work is to perform quasi-static compression tests of a single foam sample followed by two juxtaposed samples having the same dimensions. The load and displacement measurements lead to a direct extraction of the elastic constants by means of normalized stiffness and normalized stiffness ratio which depend on Poisson's ratio and shape factor. The normalized stiffness is calculated by the finite element method for different Poisson ratios. The no-slip boundary conditions imposed by the loading rigid plates create interfaces with a complex strain distribution. Beforehand, compression tests were performed by means of a standard tensile machine in order to determine the appropriate pre-compression rate for quasi-static tests. PMID:25669274
Dynamic Stiffness Analysis of Axially Loaded Timoshenko Beam with Cracks
NASA Astrophysics Data System (ADS)
Eisenberger, Moshe
2010-05-01
The structural vibratory characteristics of structural elements are affected by cracks which are found in several locations and depth along the elements. Cracks are modeled as mass less rotational springs that are characterized by their depth. Using the dynamic stiffness method it is possible to obtain a condensed reduced order system of equations without any loss of accuracy due to the size reduction. The dynamic stiffness matrices for these cases are derived from the differential equations of motion analytically, including the discontinuities introduced by the presence of the cracks. The assembly of the structural dynamic stiffness is performed in this paper by steps, i.e. after the addition of each element a condensation procedure is carried out to reduce the problem size. The condensation is performed analytically and the resulting matrix is maintained at the size of 4 by 4 matrix. After all cracked sub-elements were assembled the two end boundary restraints are introduced for the completion of the derivation. The advantages of the proposed procedure are demonstrated in several examples. In these the exact characteristic of the procedure is shown, and the results are compared to existing results in the open literature.
NASA Technical Reports Server (NTRS)
Yee, Helen M. C.; Kotov, D. V.; Wang, Wei; Shu, Chi-Wang
2013-01-01
The goal of this paper is to relate numerical dissipations that are inherited in high order shock-capturing schemes with the onset of wrong propagation speed of discontinuities. For pointwise evaluation of the source term, previous studies indicated that the phenomenon of wrong propagation speed of discontinuities is connected with the smearing of the discontinuity caused by the discretization of the advection term. The smearing introduces a nonequilibrium state into the calculation. Thus as soon as a nonequilibrium value is introduced in this manner, the source term turns on and immediately restores equilibrium, while at the same time shifting the discontinuity to a cell boundary. The present study is to show that the degree of wrong propagation speed of discontinuities is highly dependent on the accuracy of the numerical method. The manner in which the smearing of discontinuities is contained by the numerical method and the overall amount of numerical dissipation being employed play major roles. Moreover, employing finite time steps and grid spacings that are below the standard Courant-Friedrich-Levy (CFL) limit on shockcapturing methods for compressible Euler and Navier-Stokes equations containing stiff reacting source terms and discontinuities reveals surprising counter-intuitive results. Unlike non-reacting flows, for stiff reactions with discontinuities, employing a time step and grid spacing that are below the CFL limit (based on the homogeneous part or non-reacting part of the governing equations) does not guarantee a correct solution of the chosen governing equations. Instead, depending on the numerical method, time step and grid spacing, the numerical simulation may lead to (a) the correct solution (within the truncation error of the scheme), (b) a divergent solution, (c) a wrong propagation speed of discontinuities solution or (d) other spurious solutions that are solutions of the discretized counterparts but are not solutions of the governing equations. The present investigation for three very different stiff system cases confirms some of the findings of Lafon & Yee (1996) and LeVeque & Yee (1990) for a model scalar PDE. The findings might shed some light on the reported difficulties in numerical combustion and problems with stiff nonlinear (homogeneous) source terms and discontinuities in general.
Management of acute Achilles tendinopathy: effect of etoricoxib on pain control and leg stiffness.
Maquirriain, Javier; Kokalj, Antonio
2013-09-01
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
Optimal design of variable-stiffness fiber-reinforced composites using cellular automata
NASA Astrophysics Data System (ADS)
Setoodeh, Shahriar
The growing number of applications of composite materials in aerospace and naval structures along with advancements in manufacturing technologies demand continuous innovations in the design of composite structures. In the traditional design of composite laminates, fiber orientation angles are constant for each layer and are usually limited to 0, 90, and +/-45 degrees. To fully benefit from the directional properties of composite laminates, such limitations have to be removed. The concept of variable-stiffness laminates allows the stiffness properties to vary spatially over the laminate. Through tailoring of fiber orientations and laminate thickness spatially in an optimal fashion, mechanical properties of a part can be improved. In this thesis, the optimal design of variable-stiffness fiber-reinforced composite laminates is studied using an emerging numerical engineering optimization scheme based on the cellular automata paradigm. A cellular automaton (CA) based design scheme uses local update rule for both field variables (displacements) and design variables (lay-up configuration and laminate density measure) in an iterative fashion to convergence to an optimal design. In the present work, the displacements are updated based on the principle of local equilibrium and the design variables are updated according to the optimality criteria for minimum compliance design. A closed form displacement update rule for constant thickness isotropic continua is derived, while for the general anisotropic continua with variable thickness a numeric update rule is used. Combined lay-up and topology design of variable-stiffness flat laminates is performed under the action of in-plane loads and bending loads. An optimality criteria based formulation is used to obtain local design rules for minimum compliance design subject to a volume constraint. It is shown that the design rule splits into a two step application. In the first step an optimal lay-up configuration is computed and in the second step the density measure is obtained. The spatial lay-up design problem is formulated using both fiber angles and lamination parameters as design variables. A weighted average formulation is used to handle multiple load case designs. Numerical studies investigate the performance of the proposed design methodology. The optimal lay-up configuration is independent of the lattice density with more details emerging as the density is increased. Moreover, combined topology and lay-up designs are free of checkerboard patterns. (Abstract shortened by UMI.)
Singer, Madeline L.; Kobayashi, Toshiki; Lincoln, Lucas S.; Orendurff, Michael S.; Foreman, K. Bo
2014-01-01
Background Stiffness of an ankle-foot orthosis plays an important role in improving gait in patients with a history of stroke. To address this, the aim of this case series study was to determine the effect of increasing plantarflexion stiffness of an ankle-foot orthosis on the sagittal ankle and knee joint angle and moment during the first and second rockers of gait. Methods Gait data were collected in 5 subjects with stroke at a self-selected walking speed under two plantarflexion stiffness conditions (0.4 Nm/deg and 1.3 Nm/deg) using a stiffness-adjustable experimental ankle-foot orthosis on a Bertec split-belt fully instrumented treadmill in a 3-dimensional motion analysis laboratory. Findings By increasing the plantarflexion stiffness of the ankle-foot orthosis, peak plantarfexion angle of the ankle was reduced and peak dorsiflexion moment was generally increased in the first rocker as hypothesized. Two subjects demonstrated increases in both peak knee flexion angle and peak knee extension moment in the second rocker as hypothesized. The two subjects exhibited minimum contractility during active plantarflexion, while the other three subjects could actively plantarflex their ankle joint. Interpretation It was suggested that those with the decreased ability to actively plantarflex their ankle could not overcome excessive plantarflexion stiffness at initial contact of gait, and as a result exhibited compensation strategies at the knee joint. Providing excessively stiff ankle-foot orthoses might put added stress on the extensor muscles of the knee joint, potentially creating fatigue and future pathologies in some patients with stroke. PMID:25241248
Recursive calculation of Hansen coefficients
NASA Astrophysics Data System (ADS)
Branham, Richard L., Jr.
1990-06-01
Hansen coefficients are used in expansions of the elliptic motion. Three methods for calculating the coefficients are studied: Tisserand's method, the Von Zeipel-Andoyer (VZA) method with explicit representation of the polynomials required to compute the Hansen coefficients, and the VZA method with the values of the polynomials calculated recursively. The VZA method with explicit polynomials is by far the most rapid, but the tabulation of the polynomials only extends to 12th order in powers of the eccentricity, and unless one has access to the polynomials in machine-readable form their entry is laborious and error-prone. The recursive calculation of the VZA polynomials, needed to compute the Hansen coefficients, while slower, is faster than the calculation of the Hansen coefficients by Tisserand's method, up to 10th order in the eccentricity and is still relatively efficient for higher orders. The main advantages of the recursive calculation are the simplicity of the program and one's being able to extend the expansions to any order of eccentricity with ease. Because FORTRAN does not implement recursive procedures, this paper used C for all of the calculations. The most important conclusion is recursion's genuine usefulness in scientific computing.
Towards a realistic deposition coefficient expression for cirrus cloud modeling
NASA Astrophysics Data System (ADS)
Nelson, J. T.; Kay, J. E.
2007-12-01
Ice crystal deposition (condensation) coefficients affect ice crystal shape and size, two parameters that are important for cloud processes and cloud radiative impacts. Moreover, due to their effect on crystal mass uptake, deposition coefficients affect both the supersaturation at the crystal surface and the ambient supersaturation in the cloud. However, deposition coefficients are sensitive to the surface supersaturation (a fact that is widely ignored), which makes it difficult to use realistic deposition coefficient values in cloud models. The goal of our work is to find a realistic expression for the ice deposition coefficient that can be easily inserted into existing cloud models. For simplicity, we assume that only one coefficient applies to the entire surface, an assumption that gives a reasonable approximation for spherical and isometric crystal shapes. After relating the surface supersaturation to the ambient supersaturation, we determine a general expression for the deposition coefficient as a function of the ambient supersaturation and ice crystal size. Using an adiabatic parcel model with binned microphysics (Kay et al., 2006), we demonstrate the influence of a realistic deposition coefficient on ice crystal nucleation and growth.Finally, we assess if a more realistic deposition coefficient can help explain recent observations of high ice supersaturation in cirrus.
Aortic Stiffness, Blood Pressure Progression, and Incident Hypertension
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
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: 19982001; cycle 8: 20052008 [last visit: January 25, 2008]) of the Framingham Offspring study (recruited: 19711975). 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, 0.52.1] mm Hg per 1 SD; P=.002) and higher CFPWV (?, 1.5 [95% CI, 0.52.6] 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, 1.32.0] per 1 SD; P < .001), augmentation index (OR, 1.7 [95% CI, 1.42.0] per 1 SD; P < .001), and CFPWV (OR, 1.3 [95% CI, 1.01.6] 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, 1.041.46]) and lower flow-mediated dilation (OR, 0.80 [95% CI, 0.670.96]) 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. PMID:22948697
Muscular contributions to dynamic dorsoventral lumbar spine stiffness
Colloca, Christopher J.; Harrison, Deed E.; Moore, Robert J.; Gunzburg, Robert
2006-01-01
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 L3L4 interspinous space of the multifidus muscles using four stimulation frequencies (2.5, 5, 10, and 20Hz). Dynamic stiffness was quantified at rest and during muscle stimulation using a computer-controlled testing apparatus that applied variable frequency (0.4619.7Hz) 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=3.860.38N/mm at 4.0Hz; maximum ky=14.19.95N/mm at 19.7Hz). 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 3.6Hz). Compared to rest, ky during the 20Hz 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 4.91Hz (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%, 10Hz stimulus), 23/44 mechanical excitation frequencies (mean increase=10.5%, 5Hz stimulus), and 11/44 mechanical excitation frequencies (mean increase=4.16%, 2.5Hz 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. PMID:16649029
Ankle Bracing and the Neuromuscular Factors Influencing Joint Stiffness
Zinder, Steven M; Granata, Kevin P; Shultz, Sandra J; Gansneder, Bruce M
2009-01-01
Context: Health care professionals commonly prescribe external stabilization to decrease the incidence and severity of ankle sprains. The mechanism for this decrease is not clearly understood. Examining the effects of ankle bracing on biomechanical stability and influencing factors may provide important information regarding the neuromuscular effects of bracing. Objective: To study the effects of 2 different ankle braces on the neuromuscular factors influencing ankle stiffness. Design: Mixed-model repeated-measures design. Setting: Research laboratory. Patients or Other Participants: Twenty-eight physically active participants composing 2 groups: 14 with unilateral functional ankle instability (age ?=? 26.19 6.46 years, height ?=? 166.07 12.90 cm, mass ?=? 69.90 13.46 kg) and 14 with bilaterally stable ankles (age ?=? 23.76 5.82 years, height ?=? 174.00 11.67 cm, mass ?=? 68.60 13.12 kg). Intervention(s): Participants were fitted with surface electromyography electrodes over the peroneus longus, peroneus brevis, tibialis anterior, and soleus muscles. Each participant received transient motion oscillations to his or her ankle on a custom-built medial-lateral swaying cradle in each of 3 conditions: no ankle brace (NB), lace-up brace (LU), and semirigid brace (SR). Main Outcome Measure(s): Ankle stiffness as measured by the cradle and preactivation levels (percentage of maximal voluntary isometric contraction) of the 4 test muscles. Results: Stiffness levels increased across brace conditions (NB ?=? 24.79 6.59 Nm/rad, LU ?=? 28.29 7.05 Nm/rad, SR ?=? 33.22 8.78 Nm/rad; F2,52 ?=? 66.185, P < .001). No differences were found between groups for rotational stiffness (stable ?=? 27.36 6.17 Nm/rad, unstable ?=? 30.18 8.21 Nm/rad; F1,26 ?=? 1.084, P ?=? .307). Preactivation levels did not change for any of the tested muscles with the application of an ankle brace (F2,52 ?=? 1.326, P ?=? .275). Conclusions: The increase in ankle rotational stiffness with the addition of an ankle brace and the lack of any demonstrable neuromuscular changes suggested ankle braces passively contributed to the stability of the system. PMID:19593418
Kunz, S. C.
1980-01-01
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.
Actin-binding proteins sensitively mediate F-actin bundle stiffness
NASA Astrophysics Data System (ADS)
Claessens, Mireille M. A. E.; Bathe, Mark; Frey, Erwin; Bausch, Andreas R.
2006-09-01
Bundles of filamentous actin (F-actin) form primary structural components of a broad range of cytoskeletal processes including filopodia, sensory hair cell bristles and microvilli. Actin-binding proteins (ABPs) allow the cell to tailor the dimensions and mechanical properties of the bundles to suit specific biological functions. Therefore, it is important to obtain quantitative knowledge on the effect of ABPs on the mechanical properties of F-actin bundles. Here we measure the bending stiffness of F-actin bundles crosslinked by three ABPs that are ubiquitous in eukaryotes. We observe distinct regimes of bundle bending stiffness that differ by orders of magnitude depending on ABP type, concentration and bundle size. The behaviour observed experimentally is reproduced quantitatively by a molecular-based mechanical model in which ABP shearing competes with F-actin extension/compression. Our results shed new light on the biomechanical function of ABPs and demonstrate how single-molecule properties determine mesoscopic behaviour. The bending mechanics of F-actin fibre bundles are general and have implications for cytoskeletal mechanics and for the rational design of functional materials.
C, Emiliano; Longo, Stefano; Rampichini, Susanna; Devoto, Michela; Limonta, Eloisa; Venturelli, Massimo; Esposito, Fabio
2015-06-01
The study aimed to evaluate the stretch-induced changes in muscle architecture in different portions of the gastrocnemius medialis (GM) and lateralis (GL) muscles. The reliability and sensitivity of the measurements were also assessed. Fascicle length (FL) and pennation angle (PA) were calculated in the middle and distal portions of GM and GL at 0, 10 and 20 of ankle dorsiflexion. At the same angles, passive torque (Tpass), peak torque (pT) and myotendinous junction displacement of GM were determined. Stiffness was calculated at muscle-tendon unit (MTU), muscle and tendon level. After static stretching administration, Tpass, pT and MTU stiffness decreased by 22%, 12% and 16%, respectively (p<0.05). Muscle and tendon stiffness decreased by 15% and 16% (p<0.05). Nevertheless, no changes in FL and PA occurred. The reliability of the approach was always very high (intraclass correlation coefficient>0.90), with an adequate level of sensitivity. pT after static stretching was related to decreases in MTU, muscle and tendon stiffness, but not to alterations in muscle architecture. PMID:25817316
Scaling of Fluid Flow and Seismic Stiffness of Fractures
NASA Astrophysics Data System (ADS)
Petrovitch, C.; Nolte, D.; Pyrak-Nolte, L. J.
2011-12-01
A firm understanding of the relationship between the hydraulic and mechanical properties of fractures has been long sought. Seismic techniques probe the mechanical properties of fractures, e.g. fracture specific stiffness. Providing a connection between fluid flow and fracture stiffness would enable remote estimation of the flow properties in the subsurface. Linking theses two properties would improve society's ability to assess the risk related to the extraction of drinkable water, oil production, and the storage of CO2 in subsurface reservoirs. This relationship is complicated because the subsurface is composed of a hierarchy of structures and processes that span a large range of length and time scales. A scaling approach enables researchers to translate laboratory measurements towards the field scale and vise a versa. We performed a computational study of the scaling of the flow-stiffness relationship for planar fractures with uncorrelated aperture distributions. Three numerical models were required to study the scaling properties of the flow-stiffness relationship for single fractures. Firstly, the fracture topologies where constructed using a stratified continuum percolation method. Only uncorrelated fracture geometries were considered to provide a baseline of understanding for the different interacting critical thresholds occurring in the hydraulic and mechanical properties. Secondly, fracture stiffness was calculated by modeling the deformation of asperities and a deformable half space. This model computed the displacement-stress curves for a given fracture, from which the stiffness was extracted. Thirdly, due to the sensitive nature of the critical phenomena associated with fluid flow through fractures, two network flow models were used for verification. The fractures were first modeled as a network of elliptical pipes and the corresponding linear system of equations was solved. The second method consisted of using a lattice grid network, where the flow is computed using the "cubic law." Fractures were generated at five sizes (1, 0.5, 0.25, 0.125, and 0.0625m) to provide an order of magnitude variation. Each fracture was constructed such that the contact area ranged from approximately 5% to 30%. The rocks were given the properties of granite and stressed to a maximum load of 70MPa. The deformation solver was given 50 steps to reach the final load so that its flow rate could be monitored during each loading step. The results clearly showed a dependence on scale. Under low loads flow-stiffness was in an effective medium regime. However as the load increased, a distinct scale dependence emerged. This occurs because as the load increases there is an overall increase in contact area, which in turn moves the flow dynamics into a critical regime. From this finite size scaling effect, we analyzed how the uncorrelated topologies length scales changed under load to compute the flow exponents for the system. Acknowledgments: Geosciences Research Program, Office of Basic Energy Sciences US Department of Energy (DE-FG02-09ER16022), the Geo-mathematical Imaging Group at Purdue University, and the Purdue Research Foundation.
Stiffness detection and reduction in discrete stochastic simulation of biochemical systems
NASA Astrophysics Data System (ADS)
Pu, Yang; Watson, Layne T.; Cao, Yang
2011-02-01
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.
Lower-limb multi-joint stiffness of knee and ankle.
Kang, Sang Hoon; Ren, Yupeng; Xu, Dali; Zhang, Li-Qun
2014-01-01
Lower-limb multi-joint (knee and ankle) stiffness may play an important role in functional activities such as walking, and may be significantly altered post stroke. Thus, determination of lower-limb multi joint stiffness matrix is important for better understanding of gait and of pathological changes post stroke. In this study, using novel dynamics decomposition, the knee and ankle joint stiffness matrix including cross-coupled stiffness terms between the two joints were determined and reported ever first. The determined stiffness matrix may be useful for gait studies, and can be served as a baseline for studying pathophysiological changes post stroke. PMID:25570871
Torrado, Juan; Bia, Daniel; Zócalo, Yanina; Farro, Ignacio; Farro, Federico; Armentano, Ricardo L.
2012-01-01
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. PMID:22919496
Flow coefficients of monosleeve valves
NASA Technical Reports Server (NTRS)
Waldron, C D
1941-01-01
The flow coefficients of the intake and the exhaust ports of a sleeve-valve cylinder were measured by attaching the cylinder to a large tank and measuring the changes in pressure and temperature in the tank that were caused by short periods of air flow through the valve ports. The derivation of the equations on which the flow coefficients are based is given. The distribution of total pressure in the arms of the sleeve-valve intake manifold was measured. The arms are found to have as little as 75 percent of the total pressure within the manifold entrance.
Transport coefficients of fluid mixtures
Castillo, R.; de Haro, M.L.; Martina, E.
1986-07-01
On the basis of the successful description of the equilibrium properties of simple fluids and fluid mixtures using perturbation theory, the consequences of including density- and temperature-dependent diameters in the formulas for the transport coefficients of dense hard-sphere fluid mixtures are investigated. The advantages and limitations of this approach for the correlation of the experimental data of real mixtures, together with numerical estimates for particular mixtures, are discussed. On the other hand, recent mean field kinetic theories which include the effect of the attractive tail in the intermolecular potential are employed to derive transport coefficients for mixtures. Numerical results are presented and comparison with other theories is also made.
Seebeck coefficient of one electron
Durrani, Zahid A. K.
2014-03-07
The Seebeck coefficient of one electron, driven thermally into a semiconductor single-electron box, is investigated theoretically. With a finite temperature difference ?T between the source and charging island, a single electron can charge the island in equilibrium, directly generating a Seebeck effect. Seebeck coefficients for small and finite ?T are calculated and a thermally driven Coulomb staircase is predicted. Single-electron Seebeck oscillations occur with increasing ?T, as one electron at a time charges the box. A method is proposed for experimental verification of these effects.
Grosset, Jean-Franois; Lapole, Thomas; Mora, Isabelle; Verhaeghe, Martine; Doutrellot, Pierre-Louis; Prot, Chantal
2010-08-01
Clinical manual tests refer to increased ankle stiffness in children immobilized due to hip osteochondritis. The aim of the present study was to investigate musculo-articular stiffness via different techniques in immobilized children to confirm or not and quantify these observations. Ankle stiffness was quantified monthly during the long immobilization period in three diseased children and compared to healthy age-matched children. Sinusoidal perturbations were used to evaluate musculo-articular (MA) stiffness of the ankle plantar-flexors. The stiffness index (SI(MA-EMG)) was the slope of the linear relationship between angular stiffness and plantar-flexion torque normalized with electromyographic activity of the triceps surae (TS). The stiffness of the ankle plantar-flexors was also indirectly evaluated using the TS electromechanical delay (EMD). SI(MA-EMG) was greater for diseased children, and this higher stiffness was confirmed by the higher EMD values found in these immobilized children. Furthermore, both parameters indicated that ankle stiffness continues to increase through immobilization period. This study gives a quantitative evaluation of ankle stiffness changes through the immobilization period imposed to children treated for hip osteochondritis. The use of EMD measurement to indirectly evaluate these stiffness changes is also validated. This study shed for the first time some light into the patterns of muscle modifications following immobilization in children. PMID:20189829
NASA Astrophysics Data System (ADS)
Rahman, Md. Mahmudur; Lee, Donghee; Ryu, Sangjin
2013-11-01
Living cells can respond to changes in the stiffness of the surrounding matrix. Well-known examples include the durotaxis of motile cells and the stiffness-dependent differentiation of stem cells. Such mechanobiological behaviors of living cells have been investigated on hydrogel substrates of which the compliance is either static or varying in one direction. Although various techniques have been developed to fabricate hydrogel substrates of controllable stiffness distributions, however, the fabricated substrates have only hydrogel regions of varying stiffness, lacking regions of static stiffness. Therefore, it has been difficult to compare cells' responses to static stiffness and varying stiffness under the same culture condition. Thus, we aim to fabricate polyacrylamide gel substrates consisting of alternating regions of static stiffness and stiffness gradient. For controlled positioning of gel solutions with different relative concentrations of acrylamide and the crosslinker, we generated superhydrophilic regions surrounded by hydrophobic barriers on glass and then filled the regions with the gel solutions. When sandwiched by another glass surface, the gel solutions experienced limited mixing only at interfaces, which created stiffness gradients between static stiffness regions.
Long, John H; Krenitsky, Nicole M; Roberts, Sonia F; Hirokawa, Jonathan; de Leeuw, Josh; Porter, Marianne E
2011-07-01
Our goal is to describe a specific case of a general process gaining traction amongst biologists: testing biological hypotheses with biomimetic structures that operate in bioinspired robots. As an example, we present MARMT (mobile autonomous robot for mechanical testing), a surface-swimmer that undulates a submerged biomimetic tail to power cruising and accelerations. Our goal was to test the hypothesis that stiffness of the body controls swimming behavior and that both stiffness and behavior can be altered by changes in the morphology of the vertebral column. To test this hypothesis, we built biomimetic vertebral columns (BVC) outfitted with variable numbers of rigid ring centra; as the number of centra increased the axial length of the intervertebral joints decreased. Each kind of BVC was tested in dynamic bending to measure the structure's apparent stiffness as the storage and loss moduli. In addition, each kind of BVC was used as the axial skeleton in a tail that propelled MARMT. We varied MARMT's tail-beat frequency, lateral amplitude of the tail, and swimming behavior. MARMT's locomotor performance was measured using an on-board accelerometer and external video. As the number of vertebrae in the BVC of fixed length increased, so, too, did the BVC's storage modulus, the BVC's loss modulus, MARMT's mean speed during cruising, and MARMT's peak acceleration during a startle response. These results support the hypothesis that stiffness of the body controls swimming behavior and that both stiffness and behavior can be altered by changes in the morphology of the vertebral column. PMID:21576117
Direct Extraction of One-loop Integral Coefficients
Forde, Darren
2007-04-16
We present a general procedure for obtaining the coefficients of the scalar bubble and triangle integral functions of one-loop amplitudes. Coefficients are extracted by considering two-particle and triple unitarity cuts of the corresponding bubble and triangle integral functions. After choosing a specific parameterization of the cut loop momentum we can uniquely identify the coefficients of the desired integral functions simply by examining the behavior of the cut integrand as the unconstrained parameters of the cut loop momentum approach infinity. In this way we can produce compact forms for scalar integral coefficients. Applications of this method are presented for both QCD and electroweak processes, including an alternative form for the recently computed three-mass triangle coefficient in the six-photon amplitude A{sub 6}(1{sup -}, 2{sup +}, 3{sup -}, 4{sup +}, 5{sup -}, 6{sup +}). The direct nature of this extraction procedure allows for a very straightforward automation of the procedure.
Determination of absolute internal conversion coefficients using the SAGE spectrometer
NASA Astrophysics Data System (ADS)
Sorri, J.; Greenlees, P. T.; Papadakis, P.; Konki, J.; Cox, D. M.; Auranen, K.; Partanen, J.; Sandzelius, M.; Pakarinen, J.; Rahkila, P.; Uusitalo, J.; Herzberg, R.-D.; Smallcombe, J.; Davies, P. J.; Barton, C. J.; Jenkins, D. G.
2016-03-01
A non-reference based method to determine internal conversion coefficients using the SAGE spectrometer is carried out for transitions in the nuclei of 154Sm, 152Sm and 166Yb. The Normalised-Peak-to-Gamma method is in general an efficient tool to extract internal conversion coefficients. However, in many cases the required well-known reference transitions are not available. The data analysis steps required to determine absolute internal conversion coefficients with the SAGE spectrometer are presented. In addition, several background suppression methods are introduced and an example of how ancillary detectors can be used to select specific reaction products is given. The results obtained for ground-state band E2 transitions show that the absolute internal conversion coefficients can be extracted using the methods described with a reasonable accuracy. In some cases of less intense transitions only an upper limit for the internal conversion coefficient could be given.
A new correlation coefficient for bivariate time-series data
NASA Astrophysics Data System (ADS)
Erdem, Orhan; Ceyhan, Elvan; Varli, Yusuf
2014-11-01
The correlation in time series has received considerable attention in the literature. Its use has attained an important role in the social sciences and finance. For example, pair trading in finance is concerned with the correlation between stock prices, returns, etc. In general, Pearson’s correlation coefficient is employed in these areas although it has many underlying assumptions which restrict its use. Here, we introduce a new correlation coefficient which takes into account the lag difference of data points. We investigate the properties of this new correlation coefficient. We demonstrate that it is more appropriate for showing the direction of the covariation of the two variables over time. We also compare the performance of the new correlation coefficient with Pearson’s correlation coefficient and Detrended Cross-Correlation Analysis (DCCA) via simulated examples.
Nonlinear Varying Coefficient Models with Applications to Studying Photosynthesis.
Krm, Esra; Li, Runze; Wang, Yang; SEntrk, Damla
2014-03-01
Motivated by a study on factors affecting the level of photosynthetic activity in a natural ecosystem, we propose nonlinear varying coefficient models, in which the relationship between the predictors and the response variable is allowed to be nonlinear. One-step local linear estimators are developed for the nonlinear varying coefficient models and their asymptotic normality is established leading to point-wise asymptotic confidence bands for the coefficient functions. Two-step local linear estimators are also proposed for cases where the varying coefficient functions admit different degrees of smoothness; bootstrap confidence intervals are utilized for inference based on the two-step estimators. We further propose a generalized F test to study whether the coefficient functions vary over a covariate. We illustrate the proposed methodology via an application to an ecology data set and study the finite sample performance by Monte Carlo simulation studies. PMID:24976756
Miyatani, Masae; Szeto, Maggie; Moore, Cameron; Oh, Paul I.; McGillivray, Colleen F.; Catharine Craven, B.
2014-01-01
Background/Objective Elevated aortic arterial stiffness (aortic pulse wave velocity: aPWV) is an independent coronary artery disease predictor among the general population. The purpose of this study was to: (1) report aPWV values in a representative cohort of patients with spinal cord injury (SCI); (2) to compare aPWV values in people with SCI based on neurological level of injury; and (3) to contrast the reported aPWV values with available normal values for the general population. Methods Adults with chronic SCI (n=87) were divided into two groups (TETRA group, n=37 and PARA group, n=50). aPWV and potential confounders of aPWV were assessed. Analysis of covariance was used for comparisons between groups and adjusted for the confounders. Subjects aPWV values were contrasted with reference values for general population determined by The Reference value for arterial stiffness collaboration and prevalence of abnormal aPWV defined as greater than or equal to the age-specific 90th percentile was reported. Results Prevalence of abnormal aPWV in the cohort was 25.3%. After adjusting for covariates, the mean aPWV values were significantly different between two groups (TETRA: 8.0 (95% confidence interval (CI): 7.58.6) m/second, PARA: 9.0 (95% CI: 8.59.4) m/second, P=0.010). The prevalence of abnormal aPWV was significantly higher in the PARA group (36%) compared to the TETRA group (11%) (P=0.012). Conclusions One-quarter of the total cohort had an abnormal aPWV. Subjects with paraplegia had higher aPWV values and a higher frequency of abnormal aPWV than subjects with tetraplegia. Elevated aPWV in people with SCI, particularly those with paraplegia, may impart significant adverse cardiovascular consequences. PMID:25229737
Effect of Pressure on Liver Stiffness During the Development ofLiver Fibrosis in Rabbits.
Tang, Wen Bo; Xu, Qing Hua; Jiao, Zi Yu; Wu, Rong; Song, Qing; Luo, Yu Kun
2016-01-01
This study was designed to investigate whether hepatic arterial pressure and portal pressure have aneffect on liver stiffness during the development of liver fibrosis. Liver fibrosis was induced in 50 healthy New Zealand white rabbits. Laparotomy was performed to measure liver stiffness, and the portal vein and hepatic artery were successively ligated to repeat the measurements. A significant difference was observed among liverstiffness values measured at different time points (F= 22.82, p < 0.001). Differences between original liverstiffness and liver stiffness measured after portal ligation were positively correlated with portal pressure (r= 0.801, p < 0.001). In animals with grade 4 liver fibrosis, the increase in liver stiffness caused by pressure was greater than that caused by extracellular matrix accumulation (p= 0.002). In conclusion, hepatic arterial pressure and portal pressure have a significant effect on liver stiffness during the development of liver fibrosis. PMID:26497767
Aerodynamic coefficients and transformation tables
NASA Technical Reports Server (NTRS)
Ames, Joseph S
1918-01-01
The problem of the transformation of numerical values expressed in one system of units into another set or system of units frequently arises in connection with aerodynamic problems. Report contains aerodynamic coefficients and conversion tables needed to facilitate such transformation. (author)
NASA Technical Reports Server (NTRS)
Chandra, N.
1974-01-01
Numerical coefficients required to express the angular distribution for the rotationally elastic or inelastic scattering of electrons from a diatomic molecule were tabulated for the case of nitrogen and in the energy range from 0.20 eV to 10.0 eV. Five different rotational states are considered.
Some properties of Hansen's coefficients.
NASA Astrophysics Data System (ADS)
Gribanov, A. V.
Precise formulae for Hansen's coefficients X0n,m calculation when |n| ≤ 20 and |m| ≤ 20 are constructed. By using properties of the hypergeometrical function estimates of X0n,m for any higher indexes are obtained.