Whang Cho; Delbert Tesar; Robert A. Freeman
1989-01-01
A modeling procedure for a completely general kinematic system and a stiffness formulation technique for antagonistically actuated systems are given, in a format which is directly applicable to the design of high-stiffness robotic manipulator controllers. The formulation is developed in terms of kinematic influence coefficients. This involves some generalization of an existing modeling technique so that hybrid manipulator systems (combinations
A General Formulation for the Stiffness Matrix of Parallel Mechanisms
Paris-Sud XI, Université de
, numerous papers deal with the stiffness matrix (SM) of robotic manipu- lators (See section 2). HoweverA General Formulation for the Stiffness Matrix of Parallel Mechanisms Cyril Quennouelle Starting from the definition of a stiffness matrix, the authors present a new formula- tion
Generalized exclusion processes: Transport coefficients.
Arita, Chikashi; Krapivsky, P L; Mallick, Kirone
2014-11-01
A class of generalized exclusion processes with symmetric nearest-neighbor hopping which are parametrized by the maximal occupancy, k?1, is investigated. For these processes on hypercubic lattices we compute the diffusion coefficient in all spatial dimensions. In the extreme cases of k=1 (symmetric simple exclusion process) and k=? (noninteracting symmetric random walks) the diffusion coefficient is constant, while for 2?kcoefficient of self-diffusion. PMID:25493741
Generalized exclusion processes: Transport coefficients
NASA Astrophysics Data System (ADS)
Arita, Chikashi; Krapivsky, P. L.; Mallick, Kirone
2014-11-01
A class of generalized exclusion processes with symmetric nearest-neighbor hopping which are parametrized by the maximal occupancy, k ?1 , is investigated. For these processes on hypercubic lattices we compute the diffusion coefficient in all spatial dimensions. In the extreme cases of k =1 (symmetric simple exclusion process) and k =? (noninteracting symmetric random walks) the diffusion coefficient is constant, while for 2 ?k coefficient of self-diffusion.
The construction of free–free flexibility matrices as generalized stiffness inverses
C. A. Felippa; K. C. Park; M. R. Justino Filho
1998-01-01
We present generalizations of the classical structural flexibility matrix. Direct or indirect computation of flexibilities as ‘influence coefficients’ has traditionally required pre-removal of rigid body modes by imposing appropriate support conditions. Here the flexibility of an individual element or substructure is directly obtained as a particular generalized inverse of the free–free stiffness matrix. This entity is called a free–free flexibility
General frost growth mechanism on solid substrates with different stiffness.
Petit, Julien; Bonaccurso, Elmar
2014-02-01
Preventing or delaying frost formation on surfaces is of significant importance in many aspects of our daily life. Despite many efforts and improvements recently achieved in the design of new icephobic materials and substrates, not all proposed solutions are universally applicable and frost formation still remains a problem in need of further flexible solutions. In this respect, we propose to take benefit from the tunable viscoelastic properties of soft polymer gel substrates, since they are known to strongly influence the dropwise condensation process of water, and to investigate condensation frosting on them. Using polymer gels with different stiffness and a hard substrate as a reference, we demonstrate their ability to delay frost formation compared to recent results reported in the literature on other solid substrates and in particular on superhydrophobic surfaces. By investigating the frost front propagation we singled out a general behavior of its dynamic evolution consisting of two processes presenting two different time scales. This general growth appears to be independent of experimental conditions as well as substrate stiffness. PMID:24456462
NASA Technical Reports Server (NTRS)
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.
Optimization of the contact damping and stiffness coefficients to minimize human body vibration.
Amirouche, F M; Xie, M; Patwardhan, A
1994-11-01
In this paper, a lumped mass human model is used to minimize the energy absorption at the feet/hip level when the body is subjected to vertical vibration. The contact forces are assumed unknown. By coupling the dynamic response of the body with certain objective criteria, the optimum damping and stiffness coefficients of shoes/chairs are sought. The optimization technique is based on the quasi-Newton and finite-difference gradient method and is used to seek optimum coefficients of the contact forces in the solution of the body's response in the frequency domain. The criteria of acceleration, displacement and internal forces response area swept for a range of 0-15 Hz form the basis of our simulation study. In the seated/standing postures it is found that for each criteria the frequency response shifts the peak of resonance of each body segment response from 4.5/3.67 Hz to 2.5/2.255 Hz. In addition, the total energy reduces drastically when the contact conditions are optimum. The method presented in this paper is useful in modeling the medium of contacts and especially in controlling the effects of human body vibration. PMID:7869717
Bootstrap power of the generalized correlation coefficient
Reza Modarres
1996-01-01
We present a bootstrap Monte Carlo algorithm for computing the power function of the generalized correlation coefficient. The proposed method makes no assumptions about the form of the underlying probability distribution and may be used with observed data to approximate the power function and pilot data for sample size determination. In particular, the bootstrap power functions of the Pearson product
B. Audoin; C. Bescond
1997-01-01
Ultrasonic waves are generated through a composite material by means of a noncontact technique. It uses a Nd:Yag LASER for the generation and an interferometric probe for the detection of acoustic waveforms. From a suitable set of experimental data, an inversion scheme is used for the recovering of four stiffness coefficients. They characterize the elasticity in a principal plane of
Stiffness and stress characteristics of the generalized cross-spring pivot
Hongzhe Zhao; Shusheng Bi
2010-01-01
The generalized cross-spring pivot, formed by crossing two leaves symmetrically at an arbitrary position along the length, can be employed widely in precision machine due to plenty of good performances. The stiffness and stress characteristics are important consideration for this pivot, but some of these attributes have not been revealed. In this paper, a simple model for stiffness prediction is
A Method of General Stiffness Modeling for Multi-axis Machine Tool
Rong Yan; Fangyu Peng; Bin Li
2008-01-01
In this paper, a new method for computing general stiffness model at tool tip for multi-axis machine tool is presented. The\\u000a formula of general stiffness model at tool tip is derived from virtual-work principle and point transformation matrix method.\\u000a Point transformation matrix method indicates the transformation relationship of elastic displacement on both ends of flexible\\u000a axes as well as the
Path-Counting Formulas for Generalized Kinship Coefficients and Condensed Identity Coefficients
Cheng, En; Ozsoyoglu, Z. Meral
2014-01-01
An important computation on pedigree data is the calculation of condensed identity coefficients, which provide a complete description of the degree of relatedness of two individuals. The applications of condensed identity coefficients range from genetic counseling to disease tracking. Condensed identity coefficients can be computed using linear combinations of generalized kinship coefficients for two, three, four individuals, and two pairs of individuals and there are recursive formulas for computing those generalized kinship coefficients (Karigl, 1981). Path-counting formulas have been proposed for the (generalized) kinship coefficients for two (three) individuals but there have been no path-counting formulas for the other generalized kinship coefficients. It has also been shown that the computation of the (generalized) kinship coefficients for two (three) individuals using path-counting formulas is efficient for large pedigrees, together with path encoding schemes tailored for pedigree graphs. In this paper, we propose a framework for deriving path-counting formulas for generalized kinship coefficients. Then, we present the path-counting formulas for all generalized kinship coefficients for which there are recursive formulas and which are sufficient for computing condensed identity coefficients. We also perform experiments to compare the efficiency of our method with the recursive method for computing condensed identity coefficients on large pedigrees. PMID:25165486
Path-counting formulas for generalized kinship coefficients and condensed identity coefficients.
Cheng, En; Ozsoyoglu, Z Meral
2014-01-01
An important computation on pedigree data is the calculation of condensed identity coefficients, which provide a complete description of the degree of relatedness of two individuals. The applications of condensed identity coefficients range from genetic counseling to disease tracking. Condensed identity coefficients can be computed using linear combinations of generalized kinship coefficients for two, three, four individuals, and two pairs of individuals and there are recursive formulas for computing those generalized kinship coefficients (Karigl, 1981). Path-counting formulas have been proposed for the (generalized) kinship coefficients for two (three) individuals but there have been no path-counting formulas for the other generalized kinship coefficients. It has also been shown that the computation of the (generalized) kinship coefficients for two (three) individuals using path-counting formulas is efficient for large pedigrees, together with path encoding schemes tailored for pedigree graphs. In this paper, we propose a framework for deriving path-counting formulas for generalized kinship coefficients. Then, we present the path-counting formulas for all generalized kinship coefficients for which there are recursive formulas and which are sufficient for computing condensed identity coefficients. We also perform experiments to compare the efficiency of our method with the recursive method for computing condensed identity coefficients on large pedigrees. PMID:25165486
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
On Direct Computation of Beam Dynamic Stiffness Coefficients using MSC.Nastran
G. V. Narayanan
The forced frequency analysis is very important in the design of automotive structures. In particular, the Frequency Response Functions (FRF) computation is an important step in determining Noise, Vibration and Harshness (NVH) of any automotive vehicle. In general, the CAE engineer must address the severity and compliance of the design limits set in the NVH environment. Usually, a CAE engineer
Controls coefficient generalized inversion Lyapunov design for spacecraft attitude control
Abdulrahman H. Bajodah
2008-01-01
The paper introduces a controls coefficient generalized inversion attitude tracking design methodology for realization of desired linear spacecraft attitude deviation dynamics. A prescribed stable linear second order time-invariant ordinary differential equation in a spacecraft attitude deviation norm measure is evaluated along the solution trajectories of the spacecraft equations of motion, yielding a linear relation in the control variables. Generalized inversion
Warm Inflation with a General Form of the Dissipative Coefficient
Yi Zhang
2009-03-04
We propose and investigate a general form of the dissipative coefficient $\\Gamma=C_{\\phi}T^{m}/\\phi^{m-1}$ in warm inflation. We focus on discussing the strong dissipative processes $r=\\Gamma/3H\\gg1$ in the thermal state of approximate equilibrium. To this toy model, we give the slow-roll conditions, the amplitude and the index of the power spectrum under the general form of dissipative coefficient. Furthermore, the monomial potential and the hybrid-like potential are analyzed specifically. We conclude that the $m=0,3$ cases are worthy further investigation especially.
Second virial coefficient of a generalized Lennard-Jones potential
NASA Astrophysics Data System (ADS)
González-Calderón, Alfredo; Rocha-Ichante, Adrián
2015-01-01
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.
Generalized linear mixed models with varying coefficients for longitudinal data.
Zhang, Daowen
2004-03-01
The routinely assumed parametric functional form in the linear predictor of a generalized linear mixed model for longitudinal data may be too restrictive to represent true underlying covariate effects. We relax this assumption by representing these covariate effects by smooth but otherwise arbitrary functions of time, with random effects used to model the correlation induced by among-subject and within-subject variation. Due to the usually intractable integration involved in evaluating the quasi-likelihood function, the double penalized quasi-likelihood (DPQL) approach of Lin and Zhang (1999, Journal of the Royal Statistical Society, Series B61, 381-400) is used to estimate the varying coefficients and the variance components simultaneously by representing a nonparametric function by a linear combination of fixed effects and random effects. A scaled chi-squared test based on the mixed model representation of the proposed model is developed to test whether an underlying varying coefficient is a polynomial of certain degree. We evaluate the performance of the procedures through simulation studies and illustrate their application with Indonesian children infectious disease data. PMID:15032768
Frank Löffler; Roberto De Pietri; Alessandra Feo; Luca Franci; Francesco Maione
2014-11-07
We present results on the effect of the stiffness of the equation of state on the dynamical bar-mode instability in rapidly rotating polytropic models of neutron stars in full General Relativity. We determine the change in the threshold for the emergence of the instability for a range of the adiabatic $\\Gamma$ index from 2.0 to 3.0, including two values chosen to mimic more realistic equations of state at high densities.
Rafael O Alvim; Silvia RS Freitas; Noely E Ferreira; Paulo CJL Santos; Roberto S Cunha; José G Mill; José E Krieger; Alexandre C Pereira
2010-01-01
BACKGROUND: Cardiovascular diseases (CVD) are the main cause of death and disability in developed countries. In most cases, the progress of CVD is influenced by environmental factors and multifactorial inheritance. The purpose of this study was to investigate the association between APOE genotypes, cardiovascular risk factors, and a non-invasive measure of arterial stiffness in the Brazilian population. METHODS: A total
Generalized approximations of reflection coefficients in orthorhombic media
NASA Astrophysics Data System (ADS)
Zhang, Feng; Li, Xiangyang
2013-10-01
Reflection coefficients of qP- (quasi-P) and qS- (quasi-S) incident waves in orthorhombic media can be explicitly expressed by means of impedance matrices. In this paper, we extend previous studies and derive the generalized and linearized equations of reflectivity for all four types of waves in the symmetry-axis plane. These approximations have sufficient accuracy over a wide range of angles, therefore they are suitable for characterizing the seismic amplitude responses of unconventional resources. For example, they can be applied to represent the amplitude variation with offset for shale gas or coalbed methane reservoirs with strong anisotropy and complicated symmetry. Reduced equations are then derived in a transverse isotropic medium with a vertical symmetry axis (VTI) or a horizontal axis (HTI) for the anisotropic amplitude inversion. They retain higher accuracy than the corresponding previously published expressions at a strongly anisotropic interface, because they include the second-order terms of anisotropic parameters contrast. Numerical analyses on the inverse problem using different linearized expressions show the practical value of the new derived expressions in the joint inversion of the qPqP- and qPqS-waves for elastic parameters and anisotropic parameters.
General dissipation coefficient in low-temperature warm inflation
Bastero-Gil, Mar [Departamento de Física Teórica y del Cosmos, Universidad de Granada, Granada-18071 (Spain); Berera, Arjun; Rosa, João G. [SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh, EH9 3JZ (United Kingdom); Ramos, Rudnei O., E-mail: mbg@ugr.es, E-mail: ab@ph.ed.ac.uk, E-mail: rudnei@uerj.br, E-mail: joao.rosa@ed.ac.uk [Departamento de Física Teórica, Universidade do Estado do Rio de Janeiro, 20550-013 Rio de Janeiro, RJ (Brazil)
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.
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.
Aoyagi, Miki; Nagata, Kenji
2012-06-01
The term algebraic statistics arises from the study of probabilistic models and techniques for statistical inference using methods from algebra and geometry (Sturmfels, 2009 ). The purpose of our study is to consider the generalization error and stochastic complexity in learning theory by using the log-canonical threshold in algebraic geometry. Such thresholds correspond to the main term of the generalization error in Bayesian estimation, which is called a learning coefficient (Watanabe, 2001a , 2001b ). The learning coefficient serves to measure the learning efficiencies in hierarchical learning models. In this letter, we consider learning coefficients for Vandermonde matrix-type singularities, by using a new approach: focusing on the generators of the ideal, which defines singularities. We give tight new bound values of learning coefficients for the Vandermonde matrix-type singularities and the explicit values with certain conditions. By applying our results, we can show the learning coefficients of three-layered neural networks and normal mixture models. PMID:22295979
Michael W. Chevalier; Umran S. Inan
2004-01-01
A general time domain representation of the Chew and Weedon [1994] stretched coordinate perfectly matched layer (PML) absorbing boundary condition is described. This new approach mathematically operates on the spatial field derivatives and allows the PML update equations to be trivially derived from any set of general linear medium update equations. A method for calculating the frequency dependent reflection coefficient
Chains of oscillators with negative stiffness elements
NASA Astrophysics Data System (ADS)
Pasternak, Elena; Dyskin, Arcady V.; Sevel, Greg
2014-12-01
Negative stiffness is not allowed by thermodynamics and hence materials and systems whose global behaviour exhibits negative stiffness are unstable. However the stability is possible when these materials/systems are elements of a larger system sufficiently stiff to stabilise the negative stiffness elements. In order to investigate the effect of stabilisation we analyse oscillations in a chain of n linear oscillators (masses and springs connected in series) when some of the springs' stiffnesses can assume negative values. The ends of the chain are fixed. We formulated the necessary stability condition: only one spring in the chain can have negative stiffness. Furthermore, the value of negative stiffness cannot exceed a certain critical value that depends upon the (positive) stiffnesses of other springs. At the critical negative stiffness the system develops an eigenmode with vanishing frequency. In systems with viscous damping vanishing of an eigenfrequency does not yet lead to instability. Further increase in the value of negative stiffness leads to the appearance of aperiodic eigenmodes even with light damping. At the critical negative stiffness the low dissipative mode becomes non-dissipative, while for the high dissipative mode the damping coefficient becomes as twice as high as the damping coefficient of the system. A special element with controllable negative stiffness is suggested for designing hybrid materials whose stiffness and hence the dynamic behaviour is controlled by the magnitude of applied compressive force.
A generalized entering coefficient to characterize foam stability against oil in porous media
Bergeron, V.; Fagan, M.E.; Radke, C.J. [Univ. of California, Berkeley, CA (United States)
1993-12-31
Foam is a promising mobility-control fluid for improving oil recovery from porous media. Unfortunately, foams stabilized by most currently employed surfactants do not remain stable in the presence of crude oils. This work establishes that the standard criterion of a negative classical entering coefficient for oil penetration into a water/gas interface (i.e., a nonentering oil) is not pertinent for foam stability in oil-saturated porous media. This paper introduces a generalized entering coefficient that accounts for thin-film forces and capillary-suction pressure. For the first time, disjoining pressure isotherms of pseudoemulsion and foam films, surface and interfacial tensions, and steady-state pressure gradients of flowing foam in glass beadpacks with and without residual oil are measured and compared. The authors find that those surfactants which exhibit highly repulsive disjoining pressures in oil-water-gas thin films (i.e., pseudoemulision films) exhibit high negative generalized entering coefficients. These same surfactants produce foams that are insensitive to residual oil in porous media. Thus, it is the negative value of the generalized entering coefficient, as defined by the integrated disjoining pressure isotherm at the appropriate capillary pressure, and not the classical entering coefficient, that characterizes foam stability against oil.
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…
STIFFNESS SYNTHESIS OF A VARIABLE GEOMETRY PLANAR ROBOT
Nabil Simaan; Moshe Shoham
This paper addresses the problem of task-based stiffness synthesis of a variable geometry three DOF (Degrees Of Freedom) planar robot. The synthesis considers the case where the robot has a limited number of free geometric parameters and constant actuator stiffness coefficients. This defines twenty problems of stiffness synthesis, in which, three parameters of the stiffness matrix are controlled according to
Stiffness analysis of multi-fingered robot hands
H. R. Choi; W. K. Chung; Y. Youm
1993-01-01
The stiffness of a grasp is analyzed on the basis of the generalized virtual stiffness (GVS) model. Considering that the normal and lateral stiffness of the finger usually are not decoupled due to kinematics and mechanical design, GVS is formulated as coupled virtual springs. The authors relate GVS to the effective fingertip stiffness including the additional stiffness at the joint
Stiff magnetofluid cosmological model
Bali, R.; Tyagi, A.
1988-05-01
We investigate the behavior of the magnetic field in a cosmological model filled with a stiff perfect fluid in general relativity. The magnetic field is due to an electric current along the x axis. The behavior of the model when a magnetic field is absent is also discussed.
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.
RATIONALITY OF THE GENERALIZED BINOMIAL COEFFICIENTS FOR A MULTIPLICITY FREE ACTION
Benson, Chal
RATIONALITY OF THE GENERALIZED BINOMIAL COEFFICIENTS FOR A MULTIPLICITY FREE ACTION CHAL BENSON a canonical basis fp ff g for the space C [V R ] K of KÂinvariant polynoÂ mials on VR and also a basis fq ff g by the University of Missouri Research Board. 1 #12; 2 C. BENSON AND G. RATCLIFF We write the decomposition of C [V
Generalized-order perturbation with explicit coefficient for damage detection of modular beam
Chun Nam Wong; Hong-Zhong Huang; Jingqi Xiong; Hua Long Lan
2011-01-01
A general method is formulated to estimate damage location and extent from the explicit perturbation terms in specific set\\u000a of eigenvectors and eigenvalues. At first, perturbed orthonormal equation is generated from the perturbation of eigenvectors\\u000a and eigenvalues to obtain the k-th explicit perturbation coefficients. At second, perturbed eigenvalue equation is generated from the perturbation of eigenvector\\u000a and eigenvalue, and first-order
A generalized Benford's law for JPEG coefficients and its applications in image forensics
NASA Astrophysics Data System (ADS)
Fu, Dongdong; Shi, Yun Q.; Su, Wei
2007-02-01
In this paper, a novel statistical model based on Benford's law for the probability distributions of the first digits of the block-DCT and quantized JPEG coefficients is presented. A parametric logarithmic law, i.e., the generalized Benford's law, is formulated. Furthermore, some potential applications of this model in image forensics are discussed in this paper, which include the detection of JPEG compression for images in bitmap format, the estimation of JPEG compression Qfactor for JPEG compressed bitmap image, and the detection of double compressed JPEG image. The results of our extensive experiments demonstrate the effectiveness of the proposed statistical model.
Lue Xing; Zhang Haiqiang; Xu Tao; Li He [School of Science, Beijing University of Posts and Telecommunications, P.O. Box 122, Beijing 100876 (China); Tian Bo [School of Science, Beijing University of Posts and Telecommunications, P.O. Box 122, Beijing 100876 (China); State Key Laboratory of Software Development Environment, Beijing University of Aeronautics and Astronautics, Beijing 100191 (China); Key Laboratory of Information Photonics and Optical Communications (BUPT), Ministry of Education, Beijing University of Posts and Telecommunications, P.O. Box 128, Beijing 100876 (China)
2010-12-15
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.
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.
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.
NASA Astrophysics Data System (ADS)
Wang, Jia; Li, Biao; Ye, Wang-Chuan
2010-04-01
In this paper, the extended symmetry of generalized variable-coefficient Kadomtsev-Petviashvili (vcKP) equation is investigated by the extended symmetry group method with symbolic computation. Then on the basis of the extended symmetry, we can establish relation among some different kinds of vcKP equations. Thus the exact solutions of these vcKP equations can be constructed via the simple vcKP equations or constant-coefficient KP equations.
Yuxin Liu
2009-01-01
This article presents the derivation of a generic stiffness matrix for steel members accounting for the combined influence of P–delta effects, member shear deformation, inelasticity, semi-rigid connection, and joint damage. Member stiffness coefficients accounting for rotational stiffness degradation are derived using the modified moment distribution method. The displacement method is applied to derive the member stiffness coefficients due to translational
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.
Generalized entering coefficients: A criterion for foam stability against oil in porous media
Bergeron, V.; Fagan, M.E.; Radke, C.J. (Lawrence Berkeley Lab., CA (United States) Univ. of California, Berkeley, CA (United States))
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.
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.
The Spatial Stiffness Matrix from Simple Stretched Springs
Jon M. Selig
2000-01-01
Looks at the stiffness matrix of some simple but very general systems of springs supporting a rigid body. The stiffness matrix is found by symbolically differentiating the potential function. After a short example attention turns to the general structure of the stiffness matrix and in particular the principal screws introduced by Ball (1900)
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…
Averaging in damping by parametric stiffness excitation
Fadi Dohnal; Ferdinand Verhulst
2007-01-01
Stability investigations of vibration quenching employing the concept of actuators with a variable stiffness are pre- sented. Systems with an arbitrary number of degrees of freedom with linear spring- and damping-elements are considered, that are subject to self-excitation as well as parametric stiffness excitation. General conditions for full vibration suppression and conditions of instability are derived analytically by applying a
A general correlation for the local loss coefficient in Newtonian axisymmetric sudden expansions
P. J. Oliveira; F. T. Pinho; A. Schulte
1998-01-01
Results from numerical simulations and guidance from an approximated corrected-theory, developed by Oliveira and Pinho (1997), (Oliveira, P.J. and Pinho, F.T. 1997. Pressure drop coefficient of laminar Newtonian flow in axisymmetric sudden expansions. Int. J. Heat and Fluid flow 18, 518–529) have been used to arrive at a correlation expressing the irreversible loss coefficient for laminar Newtonian flow in axisymmetric
De Luca, Alessandro
in robots with elastic joints of constant stiffness [15], [16]. For some instances of 1-dof arms]. More in general, two classes of multi-dof robots with variable joint stiffness have been consideredNonlinear Decoupled Motion-Stiffness Control and Collision Detection/Reaction for the VSA
Ramón Herrera; Marco Olivares; Nelson Videla
2014-08-30
In this paper, we study a warm intermediate inflationary model with a general form for the dissipative coefficient $\\Gamma(T,\\phi)=C_\\phi\\,T^{m}/\\phi^{m-1}$ in the context of loop quantum cosmology. We examine this model in the weak and strong dissipative regimes. In general, we discuss in great detail the characteristics of this model in the slow-roll approximation. Also, we assume that the modifications to perturbation equations result exclusively from Hubble rate. In this approach, we use recent astronomical observations from Planck and BICEP2 experiments to restrict the parameters in our model.
On the Stiffness and Stiffness Control of Redundant Manipulators
Mikhail M. Svinin; Shigeyuki Hosoe; Masaru Uchiyama; Zhi Wei Luo
2002-01-01
An analysis of the stiffness of redundant manipulators is undertaken in this paper. First, the matrix of the force-dependent stiffness is derived and its basic properties are analyzed. In particular, in the planar case the stability conditions for the force dependent stiffness (and gravity-dependent stiffness) are obtained in the analytical form. Next, dual properties of the stiffness and compliance are
NASA Astrophysics Data System (ADS)
Diubin, G. N.; Korbut, A. A.
2008-09-01
For the minimization knapsack problem with Boolean variables, primal and dual greedy algorithms are formally described. Their relations to the corresponding algorithms for the maximization knapsack problem are shown. The average behavior of primal and dual algorithms for the minimization problem is analyzed. It is assumed that the coefficients of the objective function and the constraint are independent identically distributed random variables on [0, 1] with an arbitrary distribution having a density and that the right-hand side d is deterministic and proportional to the number of variables (i.e., d = ? n). A condition on ? is found under which the primal and dual greedy algorithms have an asymptotic error of t.
Robotic stiffness control and calibration as applied to human grasping tasks
Imin Kao; Mark R. Cutkosky; Roland S. Johansson
1997-01-01
In this paper, we study stiffness analysis as applied to human grasping. Grasp stiffness has been demonstrated to be useful for modeling and controlling robotic manipulators. The computation of general linear R3×3 stiffness matrices for grasping, which can be decomposed into symmetric (conservative) and asymmetric (nonconservative) components, offers physical insights for stiffness control in robotics as well as human grasping.
Ramon Herrera; Nelson Videla; Marco Olivares
2014-10-14
A warm inflationary universe scenario on a warped Dvali-Gabadadze-Porrati brane during intermediate inflation is studied. We consider a general form for the dissipative coefficient $\\Gamma(T,\\phi)\\propto T^{m}/\\phi^{m-1}$, and also study this model in the weak and strong dissipative regimes. We analyze the evolution of the universe in the slow-roll approximation, and find the exact solutions to the equations of motion. In both regimes, we utilize recent data from the BICEP2 experiment and also from the Planck satellite to constrain the parameters in our model in accordance with the theory of cosmological perturbations.
Measurement of normal contact stiffness of fractal rough surfaces
Chongpu Zhai; Sébastien Bevand; Yixiang Gan; Dorian Hanaor; Gwénaëlle Proust; Bruno Guelorget; Delphine Retraint
2014-09-03
We investigate the effects of roughness and fractality on the normal contact stiffness of rough surfaces. Samples of isotropically roughened aluminium surfaces are considered. The roughness and fractal dimension were altered through blasting using different sized particles. Subsequently, surface mechanical attrition treatment (SMAT) was applied to the surfaces in order to modify the surface at the microscale. The surface topology was characterised by interferometry based profilometry. The normal contact stiffness was measured through nanoindentation with a flat tip utilising the partial unloading method. We focus on establishing the relationships between surface stiffness and roughness, combined with the effects of fractal dimension. The experimental results, for a wide range of surfaces, showed that the measured contact stiffness depended very closely on surfaces' root mean squared (RMS) slope and their fractal dimension, with correlation coefficients of around 90\\%, whilst a relatively weak correlation coefficient of 57\\% was found between the contact stiffness and RMS roughness.
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.
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.
Adiponectin and Arterial Stiffness
Azra Mahmud; John Feely
2005-01-01
Background: Adiponectin, an anti-inflammatory adipocytokine, is reduced in hypertension, diabetes, and coronary artery disease (CAD). Arterial stiffness, as aortic pulse wave velocity (PWV) in hypertension and diabetes, and as augmentation index (AIx) in CAD, is independently associated with cardiovascular mortality. We explored the relationship between adiponectin and arterial stiffness in essential hypertension.Methods: Seventy-six untreated patients, 34 women, aged 47 ±
NASA Astrophysics Data System (ADS)
Yomba, Emmanuel; Zakeri, Gholam-Ali
2013-12-01
We introduce an approach that combines a similarity method with several transformations to find analytical solitary wave solutions for a generalized space- and time-variable coefficients of nonlinear Schrödinger equation with higher-order terms with consideration of varying dispersion, higher nonlinearities, gain/loss and external potential. One of these transformations is constructed in such a way that allows study of the width of localized solutions. Solitary-like wave solutions for front, bright and dark are given. The precise expressions of the soliton's width, peak, and the trajectory of its mass center and the external potential which are symbol of dynamic behavior of these solutions, are investigated analytically. In addition, the dynamical behavior of moving, periodic, quasi-periodic of breathing, and resonant are discussed. Stability of the obtained solutions is analyzed both analytically and numerically.
Lindsey, William Todd
1993-01-01
to an eccentricity ratio of 0. 5. Results show that the direct stiffness generally increases for a converging taper and decreases with a diverging taper. Other coefficients decrease with increasing convergent and divergent taper. Test results show static... XIa. Mass coefficients; slightly convergent seal eccentric tests . . Uncertainties for mass coefficients; slightly convergent seal 78 eccentric tests 79 XIIb. Flowrate, average temperature, minimum radial clearance, and whirl-frequency ratio...
NASA Astrophysics Data System (ADS)
Petrishcheva, E.; Abart, R.
2012-04-01
We address mathematical modeling and computer simulations of phase decomposition in a multicomponent system. As opposed to binary alloys with one common diffusion parameter, our main concern is phase decomposition in real geological systems under influence of strongly different interdiffusion coefficients, as it is frequently encountered in mineral solid solutions with coupled diffusion on different sub-lattices. Our goal is to explain deviations from equilibrium element partitioning which are often observed in nature, e.g., in a cooled ternary feldspar. To this end we first adopt the standard Cahn-Hilliard model to the multicomponent diffusion problem and account for arbitrary diffusion coefficients. This is done by using Onsager's approach such that flux of each component results from the combined action of chemical potentials of all components. In a second step the generalized Cahn-Hilliard equation is solved numerically using finite-elements approach. We introduce and investigate several decomposition scenarios that may produce systematic deviations from the equilibrium element partitioning. Both ideal solutions and ternary feldspar are considered. Typically, the slowest component is initially "frozen" and the decomposition effectively takes place only for two "fast" components. At this stage the deviations from the equilibrium element partitioning are indeed observed. These deviations may became "frozen" under conditions of cooling. The final equilibration of the system occurs on a considerably slower time scale. Therefore the system may indeed remain unaccomplished at the observation point. Our approach reveals the intrinsic reasons for the specific phase separation path and rigorously describes it by direct numerical solution of the generalized Cahn-Hilliard equation.
C. C. Briggs
2000-08-03
This paper presents some possible features of general expressions for Lovelock tensors and for the coefficients of Lovelock Lagrangians up to the 15th order in curvature (and beyond) in terms of the Riemann-Christoffel and Ricci curvature tensors and the Riemann curvature scalar for n-dimensional differentiable manifolds having a general linear connection.
Stochastic dynamics with fatigue-induced stiffness degradation
K. Sobczyk; J. Trebicki
2000-01-01
This article deals with stochastic dynamics coupled with simultaneous evolution of degradation of the system properties. We provide a general formulations and interpretations of various response-degradation problems associated with randomly vibrating systems and then an efficient analysis of vibratory systems with fatigue-induced stiffness degradation is presented. First, an approach to the random vibration problem with empirical characterization of stiffness degradation
Geometric Characteristics of Antagonistic Stiffness in Redundantly Actuated Mechanisms
Byung-ju Yi; Robert A. Freeman
1993-01-01
Parallel closed-chain mechanical architectures allow for redundant actuation in the force domain. Antagonistic actuation, afforded by this input force redundancy, in conjunction with nonlinear linkage geometry, creates an effective stiffness directly analogous to that of a wound metal spring. A general stiffness model for such systems is derived, and it is shown that the constitutive relationship between actuation effort and
Cartesian stiffness matrix of manipulators with passive joints: Analytical approach
Anatoly Pashkevich; Alexandr Klimchik; Stéphane Caro; Damien Chablat
2011-01-01
? Abstract—The paper focuses on stiffness matrix computation for manipulators with passive joints. It proposes both explicit analytical expressions and an efficient recursive procedure that are applicable in general case and allow obtaining the desired matrix either in analytical or numerical form. Advantages of the developed technique and its ability to produce both singular and non-singular stiffness matrices are illustrated
Stiffness matrix method for foot force distribution of walking vehicles
X. C. Gao; S. M. Song
1990-01-01
A general method, called the stiffness matrix method, is developed to determine the foot forces of walking vehicles, taking into account the elasticity of the leg structures, the actuating systems, and the terrain. Also derived are the analytical expressions of the stiffness matrix for the popular pantograph-type legs when only the leg elasticity is considered. The method is effective and
Cartesian stiffness matrix of manipulators with passive joints: Analytical approach
A. Pashkevich; A. Klimchik; S. Caro; D. Chablat
2011-01-01
The paper focuses on stiffness matrix computation for manipulators with passive joints. It proposes both explicit analytical expressions and an efficient recursive procedure that are applicable in general case and allow obtaining the desired matrix either in analytical or numerical form. Advantages of the developed technique and its ability to produce both singular and non-singular stiffness matrices are illustrated by
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.
Transfer having a coupling coefficient higher than its active material
NASA Technical Reports Server (NTRS)
Lesieutre, George A. (Inventor); Davis, Christopher L. (Inventor)
2001-01-01
A coupling coefficient is a measure of the effectiveness with which a shape-changing material (or a device employing such a material) converts the energy in an imposed signal to useful mechanical energy. Device coupling coefficients are properties of the device and, although related to the material coupling coefficients, are generally different from them. This invention describes a class of devices wherein the apparent coupling coefficient can, in principle, approach 1.0, corresponding to perfect electromechanical energy conversion. The key feature of this class of devices is the use of destabilizing mechanical pre-loads to counter inherent stiffness. The approach is illustrated for piezoelectric and thermoelectrically actuated devices. The invention provides a way to simultaneously increase both displacement and force, distinguishing it from alternatives such as motion amplification, and allows transducer designers to achieve substantial performance gains for actuator and sensor devices.
T. Qureshi; S. N. Bhattacharya
2006-01-01
We present a new approach to evaluate phase and group velocities of Love and Rayleigh waves in a spherical layered earth using the generalized reflection-transmission coefficient method. The approach is simple and self-efficient to give numerically stable results at all frequency ranges. The method has been previously used for computing phase velocities in a flat layered earth. For spherical earth,
Xiangrong Li; Dafa Li
2012-05-04
We solve the entanglement classification under stochastic local operations and classical communication (SLOCC) for general n-qubit states. For two arbitrary pure n-qubit states connected via local operations, we establish an equation between the two coefficient matrices associated with the states. The rank of the coefficient matrix is preserved under SLOCC and gives rise to a simple way of partitioning all the pure states of n qubits into different families of entanglement classes, as exemplified here. When applied to the symmetric states, this approach reveals that all the Dicke states |l,n> with l=1, ..., [n/2] are inequivalent under SLOCC.
Extraordinary stiffness tunability through thermal expansion of nonlinear defect modes
Marc Serra-Garcia; Joseph Lydon; Chiara Daraio
2014-11-19
Incremental stiffness characterizes the variation of a material's force response to a small deformation change. Typically materials have an incremental stiffness that is fixed and positive, but recent technologies, such as super-lenses, low frequency band gap materials and acoustic cloaks, are based on materials with zero, negative or extremely high incremental stiffness. So far, demonstrations of this behavior have been limited either to a narrow range of frequencies, temperatures, stiffness or to specific deformations. Here we demonstrate a mechanism to tune the static incremental stiffness that overcomes those limitations. This tunability is achieved by driving a nonlinear defect mode in a lattice. As in thermal expansion, the defect's vibration amplitude affects the force at the boundary, hence the lattice's stiffness. By using the high sensitivities of nonlinear systems near bifurcation points, we tune the magnitude of the incremental stiffness over a wide range: from positive, to zero, to arbitrarily negative values. The particular deformation where the incremental stiffness is modified can be arbitrarily selected varying the defect's driving frequency. We demonstrate this experimentally in a compressed array of spheres and propose a general theoretical model.
Variable mechanical stiffness control based on human stiffness estimation
Chowarit Mitsantisuk; Kiyoshi Ohishi; Seiichiro Katsura
2011-01-01
Control of the human-robot interaction system presents many challenges, which include the consideration in terms of the properties of human operators, sensor device, and linkage mechanisms of the robot. This paper presents the application of a variable mechanical stiffness control based on a human stiffness estimation. In the controller design, dual disturbance observers with respect to two operation modes, namely
Averaging in damping by parametric stiffness excitation Fadi Dohnal a
Verhulst, Ferdinand
to Elsevier 27 August 2007 #12;respectively, where x represents a deflection and c is a negative damping by a negative damping coefficient. It should be noted that linearisation works well for a descriptionAveraging in damping by parametric stiffness excitation Fadi Dohnal a , Ferdinand Verhulst b a
“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
NSDL National Science Digital Library
A feature at Public Broadcasting Service's Web Lab, this site offers tales and advice from the front lines of working America. The Workplace Diaries section offers daily updates from the "Work-A-Day World." Diarists include a Northwest customer service rep, a Midwest teacher, an Illinois casino worker, and a Midwest utility worker. The Free Advice section allows users to submit workplace troubles to the site's expert problem-solver. Current Feature Articles include a guide to interoffice romance and a discussion of worker privacy in the workplace. Additional offerings at the site include a worker forum, Stress-O-Meter, and the Working Stiff Action Guide, which contains information on workplace activism.
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
Nonlinear vibration of thick stiff fabric with small flexural stiffness
NASA Astrophysics Data System (ADS)
Chen, J.-P.; Wang, S.-Z.; Wu, W.-Y.; Gu, H.-B.
2008-02-01
Dynamic behaviour of fabric is very complex during weaving, dyeing and finishing processes. Thick stiff fabric vibration has great influence not only on the fabric itself but also on the performance of machine. The theoretic analysis for the nonlinear free vibration of thick stiff fabric with small flexural stiffness is put forward in the paper. The nonlinear partial differential equation is derived by applying the flexible thin plate theory, and then transformed into nonlinear ordinary differential equation by the Galerkin method. The approximate analytical solution is obtained by the homotopy perturbation method.
The stiffness matrix in elastically articulated rigid-body systems
J. Kövecses; J. Angeles
2007-01-01
Discussed in this paper is the Cartesian stiffness matrix, which recently has received special attention within the robotics\\u000a research community. Stiffness is a fundamental concept in mechanics; its representation in mechanical systems whose potential\\u000a energy is describable by a finite set of generalized coordinates takes the form of a square matrix that is known to be, moreover,\\u000a symmetric and positive-definite
Stiffness of desiccating insect wings.
Mengesha, T E; Vallance, R R; Mittal, R
2011-03-01
The stiffness of insect wings is typically determined through experimental measurements. Such experiments are performed on wings removed from insects. However, the wings are subject to desiccation which typically leads to an increase in their stiffness. Although this effect of desiccation is well known, a comprehensive study of the rate of change in stiffness of desiccating insect wings would be a significant aid in planning experiments as well as interpreting data from such experiments. This communication presents a comprehensive experimental analysis of the change in mass and stiffness of gradually desiccating forewings of Painted Lady butterflies (Vanessa?cardui). Mass and stiffness of the forewings of five butterflies were simultaneously measured every 10 min over a 24 h period. The averaged results show that wing mass declined exponentially by 21.1% over this time period with a time constant of 9.8 h, while wing stiffness increased linearly by 46.2% at a rate of 23.4 µN mm(-1) h(-1). For the forewings of a single butterfly, the experiment was performed over a period of 1 week, and the results show that wing mass declined exponentially by 52.2% with a time constant of 30.2 h until it reached a steady-state level of 2.00 mg, while wing stiffness increased exponentially by 90.7% until it reached a steady-state level of 1.70 mN mm(-1). PMID:21160117
Chakraborty, Sushmita; Nandy, Sudipta; Barthakur, Abhijit
2015-02-01
We investigate coupled nonlinear Schrödinger equations (NLSEs) with variable coefficients and gain. The coupled NLSE is a model equation for optical soliton propagation and their interaction in a multimode fiber medium or in a fiber array. By using Hirota's bilinear method, we obtain the bright-bright, dark-bright combinations of a one-soliton solution (1SS) and two-soliton solutions (2SS) for an n-coupled NLSE with variable coefficients and gain. Crucial properties of two-soliton (dark-bright pair) interactions, such as elastic and inelastic interactions and the dynamics of soliton bound states, are studied using asymptotic analysis and graphical analysis. We show that a bright 2-soliton, in addition to elastic interactions, also exhibits multiple inelastic interactions. A dark 2-soliton, on the other hand, exhibits only elastic interactions. We also observe a breatherlike structure of a bright 2-soliton, a feature that become prominent with gain and disappears as the amplitude acquires a minimum value, and after that the solitons remain parallel. The dark 2-soliton, however, remains parallel irrespective of the gain. The results found by us might be useful for applications in soliton control, a fiber amplifier, all optical switching, and optical computing. PMID:25768629
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.
Switchable stiffness scanning microscope probe
Mueller-Falcke, Clemens T. (Clemens Tobias)
2005-01-01
Atomic Force Microscopy (AFM) has rapidly gained widespread utilization as an imaging device and micro/nano-manipulator during recent years. This thesis investigates the new concept of a dual stiffness scanning probe with ...
NASA Astrophysics Data System (ADS)
Herrera, Ramón; Videla, Nelson; Olivares, Marco
2015-05-01
A warm inflationary Universe in the Randall-Sundrum II model during intermediate inflation is studied. For this purpose, we consider the general form for the dissipative coefficient , and also we analyze this inflationary model in the weak and strong dissipative regimes. We study the evolution of the Universe under the slow-roll approximation and find solutions to the full effective Friedmann equation in the brane-world framework. In order to constrain the parameters in our model, we consider the recent data from the BICEP2 to Planck 2015 data together with the necessary condition for warm inflation , and also the condition from the weak (or strong) dissipative regime.
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-Bäcklund 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-Bäcklund 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.
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 Painlevé-integrable conditions are given out by Painlevé test, and an auto-Bäcklund transformation is presented via the truncated Painlevé expansion. Under the integrable condition and auto-Bäcklund transformation, the analytic solutions are provided, including the soliton-like, periodic and rational solutions. Lax pair, Riccati-type auto-Bäcklund transformation (R-BT) and Wahlquist–Estabrook-type auto-Bäcklund 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)
Nadeem, Qurrat-Ul-Ain; Kammoun, Abla; Debbah, Merouane; Alouini, Mohamed-Slim
2015-07-01
Previous studies have confirmed the adverse impact of fading correlation on the mutual information (MI) of two-dimensional (2D) multiple-input multiple-output (MIMO) systems. More recently, the trend is to enhance the system performance by exploiting the channel's degrees of freedom in the elevation, which necessitates the derivation and characterization of three-dimensional (3D) channels in the presence of spatial correlation. In this paper, an exact closed-form expression for the Spatial Correlation Function (SCF) is derived for 3D MIMO channels. This novel SCF is developed for a uniform linear array of antennas with nonisotropic antenna patterns. The proposed method resorts to the spherical harmonic expansion (SHE) of plane waves and the trigonometric expansion of Legendre and associated Legendre polynomials. The resulting expression depends on the underlying arbitrary angular distributions and antenna patterns through the Fourier Series (FS) coefficients of power azimuth and elevation spectrums. The novelty of the proposed method lies in the SCF being valid for any 3D propagation environment. The developed SCF determines the covariance matrices at the transmitter and the receiver that form the Kronecker channel model. In order to quantify the effects of correlation on the system performance, the information-theoretic deterministic equivalents of the MI for the Kronecker model are utilized in both mono-user and multi-user cases. Numerical results validate the proposed analytical expressions and elucidate the dependence of the system performance on azimuth and elevation angular spreads and antenna patterns. Some useful insights into the behaviour of MI as a function of downtilt angles are provided. The derived model will help evaluate the performance of correlated 3D MIMO channels in the future.
Discher, Dennis
RA + + envelope associated LMNA YAP1 SRF+ nuclear Actin LMNA + Stress stabilized assembly of LMNA : LMNA message P : LMNA protein 1) Lamin-A and collagen levels scale with tissue stiffness 3) Matrix coiled-coil U251 A549 LMNA-OE A549 1 20 3 4 Distinct nuclei AggregationDisrupted lamina & chromatin Shear
Positive Association Between Adipose Tissue and Bone Stiffness.
Berg, R M; Wallaschofski, H; Nauck, M; Rettig, R; Markus, M R P; Laqua, R; Friedrich, N; Hannemann, A
2015-07-01
Obesity is often considered to have a protective effect against osteoporosis. On the other hand, several recent studies suggest that adipose tissue may have detrimental effects on bone quality. We therefore aimed to investigate the associations between body mass index (BMI), waist circumference (WC), visceral adipose tissue (VAT) or abdominal subcutaneous adipose tissue (SAT), and bone stiffness. The study involved 2685 German adults aged 20-79 years, who participated in either the second follow-up of the population-based Study of Health in Pomerania (SHIP-2) or the baseline examination of the SHIP-Trend cohort. VAT and abdominal SAT were quantified by magnetic resonance imaging. Bone stiffness was assessed by quantitative ultrasound (QUS) at the heel (Achilles InSight, GE Healthcare). The individual risk for osteoporotic fractures was determined based on the QUS-derived stiffness index and classified in low, medium, and high risk. Linear regression models, adjusted for sex, age, physical activity, smoking status, risky alcohol consumption, diabetes, and height (in models with VAT or abdominal SAT as exposure), revealed positive associations between BMI, WC, VAT or abdominal SAT, and the QUS variables broadband-ultrasound attenuation or stiffness index. Moreover, BMI was positively associated with speed of sound. Our study shows that all anthropometric measures including BMI and, WC as well as abdominal fat volume are positively associated with bone stiffness in the general population. As potential predictors of bone stiffness, VAT and abdominal SAT are not superior to easily available measures like BMI or WC. PMID:25929703
Tube width fluctuations of entangled stiff polymers
Jens Glaser; Klaus Kroy
2011-09-29
The tube-like cages of stiff polymers in entangled solutions have been shown to exhibit characteristic spatial heterogeneities. We explain these observations by a systematic theory generalizing previous work by D. Morse (Phys. Rev. E 63:031502, 2001). With a local version of the binary collision approximation (BCA), the distribution of confinement strengths is calculated, and the magnitude and the distribution function of tube radius fluctuations are predicted. Our main result is a unique scaling function for the tube radius distribution, in good agreement with experimental and simulation data.
A simple theory of geometrical stiffness with applications to beam and shell problems
J. H. Argyrls; P. C. Dunne
Geometrical stiffness is the basis for any attempt to study the behaviour of slender beams and thin shells under conditions\\u000a in which large deflections may occur with small strains. Not all problems require high accuracy in the representation of the\\u000a geometrical stiffness. These are generally certain self-equilibrating stress systems (natural modes) which are the principal\\u000a contributors to the geometrical stiffness.
Variable stiffness torsion springs
Dean C. Alhorn; Michael E. Polites
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
Variable stiffness torsion springs
Dean C. Alhorn; Michael E. Polites
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
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.
Herrera, Ramón; Olivares, Marco
2015-01-01
A warm inflationary Universe in the Randall-Sundrum II model during intermediate inflation is studied. For this purpose, we consider a general form for the dissipative coefficient $\\Gamma(T,\\phi)=C_{\\phi}\\,\\frac{T^{m}}{\\phi^{m-1}}$, and also analyze this inflationary model in the weak and strong dissipative regimes. We study the evolution of the Universe under the slow-roll approximation and find solutions to the full effective Friedmann equation in the brane-world framework. In order to constrain the parameters in our model, we consider the recent data from the BICEP2-Planck 2015 data together with the necessary condition for warm inflation $T>H$, and also the condition from the weak (or strong) dissipative regime.
Ramón Herrera; Nelson Videla; Marco Olivares
2015-04-28
A warm inflationary Universe in the Randall-Sundrum II model during intermediate inflation is studied. For this purpose, we consider a general form for the dissipative coefficient $\\Gamma(T,\\phi)=C_{\\phi}\\,\\frac{T^{m}}{\\phi^{m-1}}$, and also analyze this inflationary model in the weak and strong dissipative regimes. We study the evolution of the Universe under the slow-roll approximation and find solutions to the full effective Friedmann equation in the brane-world framework. In order to constrain the parameters in our model, we consider the recent data from the BICEP2-Planck 2015 data together with the necessary condition for warm inflation $T>H$, and also the condition from the weak (or strong) dissipative regime.
Dynamic stiffness and damping of externally pressurized gas lubricated journal bearings
NASA Technical Reports Server (NTRS)
Fleming, D. P.; Thayer, W. J.; Cunningham, R. E.
1976-01-01
A rigid vertical shaft was operated with known amounts of unbalance at speeds up to 30,000 rpm and gas supply pressure ratios to 4.8. From measured amplitude and phase angle data, dynamic stiffness and damping coefficients of the bearings were determined. The measured stiffness was proportional to the supply pressure, while damping was little affected by supply pressure. Damping dropped rapidly as the fractional frequency whirl threshold was approached. A small eccentricity analysis overpredicted the stiffness by 4 to 55 percent. Predicted damping was close to measured at low speeds but higher at high speeds
Geometric Design Tools for Stiffness and Vibration Analysis of Robotic Mechanisms
Jin Wook Kim; Frank C. Park; Munsang Kim
2000-01-01
We present a methodology for the first-order stiffness and vibration analysis of general robotic systems including parallel mechanisms, based on geometric methods for kinematics and elasticity analysis. We exploit the uniformity and structure typically extant in parallel mechanisms to develop an accurate and computationally tractable method of stiffness and vibration analysis that is amenable 60 design iterations and optimization. By
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.
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
Reduced-Stiffness Method in the Theory of Shells
G. D. Gavrilenko; J. G. A. Croll
2004-01-01
The fundamentals of the reduced-stiffness method, which is used in buckling analysis of reinforced and perfect and imperfect nonreinforced shells, are set out. The method is validated analytically and experimentally. The lower bound determined by this method is very close to the experimental lower bound. Some aspects of the current state and prospects for development and generalization of the method
The eigenscrew decomposition of spatial stiffness matrices
Shuguang Huang; Joseph M. Schimmels
2000-01-01
A manipulator system is modeled as a kinematically unconstrained rigid body suspended by elastic devices. The structure of spatial stiffness is investigated by evaluating the stiffness matrix “primitives”-the rank-1 matrices that compose a spatial stiffness matrix. Although the decomposition of a rank-2 or higher stiffness matrix into the sum of rank-1 matrices is not unique, one property of the set
Response of initial field to stiffness perturbation
Chen-Wu Wu
2014-03-19
Response of initial elastic field to stiffness perturbation and its possible application is investigated. Virtual thermal softening is used to produce the stiffness reduction for demonstration. It is interpreted that the redistribution of the initial strain will be developed by the non-uniform temperature elevation, as which leads to the non-uniform reduction of the material stiffness. Therefore, the initial filed is related to the stiffness perturbation and incremental field in a matrix form after eliminating the thermal expansion effect.
COMMUNICATION Stiffness of desiccating insect wings
T. E. Mengesha; R. R. Vallance; R. Mittal
2011-01-01
The stiffness of insect wings is typically determined through experimental measurements. Such experiments are performed on wings removed from insects. However, the wings are subject to desiccation which typically leads to an increase in their stiffness. Although this effect of desiccation is well known, a comprehensive study of the rate of change in stiffness of desiccating insect wings would be
Zero Stiffness Tensegrity Structures M. Schenk a
Guest, Simon
Zero Stiffness Tensegrity Structures M. Schenk a S.D. Guest b, J.L. Herder a aMechanical, Maritime members with a zero rest length allow the construction of tensegrity struc- tures that are in equilibrium, they have zero stiffness. The zero-stiffness modes are not internal mechanisms, as they involve first
Stiffness Analysis of Overconstrained Parallel Manipulators
Paris-Sud XI, Université de
equations for the unloaded manipulator configuration, which allows computing the stiffness matrix mechanisms, Stiffness modeling, Parallelogram-based linkage, Orthoglide robot 1. Introduction Parallel-effector. Numerically, this property is defined through the "stiffness matrix" K, which gives the relation between
Stiffness Performance of Multibody Robotic Systems
Giuseppe Carbone
2006-01-01
Stiffness can be considered of primary importance in order to guarantee the successful use of any robotic system for a given task. Therefore, this paper proposes procedures for carrying out both numerical and experimental estimations of stiffness performance for multibody robotic systems. The numerical procedure is based on models with lumped parameters for deriving the Cartesian stiffness matrix. The experimental
Akagi, Ryota; Kusama, Saki
2015-08-01
The goals of this study were to compare neck and shoulder stiffness values determined by shear wave ultrasound elastography with those obtained with a muscle hardness meter and to verify the correspondence between objective and subjective stiffness in the neck and shoulder. Twenty-four young men and women participated in the study. Their neck and shoulder stiffness was determined at six sites. Before the start of the measurements, patients rated their present subjective symptoms of neck and shoulder stiffness on a 6-point verbal scale. At all measurement sites, the correlation coefficients between the values of muscle hardness indices determined by the muscle hardness meter and shear wave ultrasound elastography were not significant. Furthermore, individuals' subjective neck and shoulder stiffness did not correspond to their objective symptoms. These results suggest that the use of shear wave ultrasound elastography is essential to more precisely assess neck and shoulder stiffness. PMID:25944285
Stiffness analysis of corrugated flexure beam used in compliant mechanisms
NASA Astrophysics Data System (ADS)
Wang, Nianfeng; Liang, Xiaohe; Zhang, Xianmin
2015-05-01
Conventional flexible joints generally have limited range of motion and high stress concentration. To overcome these shortcomings, corrugated flexure beam(CF beam) is designed because of its large flexibility obtained from longer overall length on the same span. The successful design of compliant mechanisms using CF beam requires manipulation of the stiffnesses as the design variables. Empirical equations of the CF beam stiffness components, except of the torsional stiffness, are obtained by curve-fitting method. The application ranges of all the parameters in each empirical equation are also discussed. The ratio of off-axis to axial stiffness is considered as a key characteristic of an effective compliant joint. And parameter study shows that the radius of semi-circular segment and the length of straight segment contribute most to the ratio. At last, CF beam is used to design translational and rotational flexible joints, which also verifies the validity of the empirical equations. CF beam with large flexibility is presented, and empirical equations of its stiffness are proposed to facilitate the design of flexible joint with large range of motion.
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 applic
Estimation of Quasi-Stiffness of the Human Knee in the Stance Phase of Walking
Shamaei, Kamran; Sawicki, Gregory S.; Dollar, Aaron M.
2013-01-01
Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as prostheses and orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75–2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R2 > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking. PMID:23533662
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.
Enhanced Stiffness Modeling, Identification and Characterization for Robot Manipulators
Gürsel Alici; Bijan Shirinzadeh
2005-01-01
This paper presents the enhanced stiffness modeling and analysis of robot manipulators, and a methodology for their stiffness identification and characterization. Assuming that the manipulator links are infinitely stiff, the enhanced stiffness model contains: 1) the passive and active stiffness of the joints and 2) the active stiffness created by the change in the manipulator configuration, and by external force
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
Modifiable risk factors for increased arterial stiffness in outpatient nephrology.
Elewa, Usama; Fernandez-Fernandez, Beatriz; Alegre, Raquel; Sanchez-Niño, Maria D; Mahillo-Fernández, 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). Mean±SD Delta PWV was 0.76±1.60 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
Diamond's elastic stiffnesses from 322 K to 10 K
NASA Astrophysics Data System (ADS)
Migliori, Albert; Ledbetter, Hassel; Leisure, Robert G.; Pantea, C.; Betts, J. B.
2008-09-01
Using resonant-ultrasound spectroscopy, we measured diamond's monocrystal elastic-stiffness coefficients C11, C12, and C44, between 322 and 10 K. Changes are small and smooth: The bulk modulus B =(C11+2C12)/3 increases about 1 part in 1000, describable by a quasiharmonic Einstein-oscillator model. Zero-temperature Cij correspond to a 2244-K Debye characteristic temperature. Using a low-temperature form of the Grüneisen-Debye model, we calculated an overall thermodynamic Grüneisen parameter of ? =1.26; using a high-temperature form we calculated 0.71; the lattice specific heat yields ? =1.10.
Cha, Gene
2013-11-07
High stiffness / low mass materials or structures reduce structure weight in transportation, but show little inherent damping. A new composite material that exhibits high stiffness and high damping might reduce issues with ...
Infinitely stiff composite via a rotation-stabilized negative-stiffness phase
NASA Astrophysics Data System (ADS)
Kochmann, D. M.; Drugan, W. J.
2011-07-01
We show that an elastic composite material having a component with sufficiently negative stiffness to produce positive-infinite composite stiffness can be stabilized by the gyroscopic forces produced by composite rotation.
Vibration transmission through rolling element bearings, part I: Bearing stiffness formulation
NASA Astrophysics Data System (ADS)
Lim, T. C.; Singh, R.
1990-06-01
Current bearing models, based on either ideal boundary condition or purely translational stiffness element description, cannot explain how the vibratory motion may be transmitted from the rotating shaft to the casing and other connecting structures in rotating mechanical equipment. For example, a vibration model of a rotating system based upon the existing bearing models can predict only the purely in-plane type motion on the flexible casing plate given only the bending motion on the shaft. However, experimental results have shown that the casing plate motion is primarily flexural or out-of-plane type. In this paper this issue is claridied quantitatively and qualitatively by developing a new mathematical model for the precision rolling element bearings from basic principles. A comprehensive bearing stiffness matrix [ K] bm of dimension six is proposed which clearly demonstrates a coupling between the shaft bending motion and the flexural motion on the casing plate. A numerical scheme which involves a solution of non-linear algebraic equations is proposed for the estimation of the stiffness coefficients given the mean bearing load vector. A second method which requires the direct evaluation of these stiffness coefficients given the mean bearing displacement vector is also discussed. Some of the translational stiffness coefficients of the proposed bearing matrix have been verified by using available analytical and experimental data. Further validation of [ K] bm is not possible as coupling coefficients are never measured. Also, parametric studies on the effect of unloaded contact angle, preload or bearing type are included. These results lead to a complete characterization of the bearing stiffness matrix. The theory is used to analyze vibration transmission properties in the companion paper, Part II.
Analysis of the evaporation coefficient and the condensation coefficient of water
R. Marek; J. Straub
2001-01-01
The evaporation and condensation coefficients of water are extensively analyzed considering also data hitherto not taken into account. From the performed evaluation, a decline of both coefficients with increasing temperature and pressure is derived. For water, the condensation coefficients is generally higher than the evaporation coefficient. Evaporation and condensation coefficients exceed 0.1 for dynamically renewing water surfaces, while the analysis
Lakes, Roderic
Advanced damper with high stiffness and high hysteresis damping based on negative structural online 8 April 2013 Keywords: Damping Stiffness Columns Buckling Uniaxial Compression Experimental techniques Structures a b s t r a c t High structural damping combined with high stiffness is achieved
On Zero Stiffness Mark Schenk and Simon D Guest
Guest, Simon
preprint On Zero Stiffness Mark Schenk and Simon D Guest Abstract Zero stiffness structures have and iv) zero stiffness. Each perspective on zero stiffness provides different methods of analysis and design. This paper reviews the concept of zero stiffness and categorises examples from the literature
Mechanisms, Pathophysiology, and Therapy of Arterial Stiffness
Susan J. Zieman; Vojtech Melenovsky; David A. Kass
2010-01-01
Arterial stiffness is a growing epidemic associated with increased risk of cardiovascular events, dementia, and death. Decreased compliance of the central vasculature alters arterial pressure and flow dynamics and impacts cardiac performance and coronary perfusion. This article reviews the structural, cellular, and genetic contributors to arterial stiffness, including the roles of the scaffolding proteins, extracellular matrix, inflammatory molecules, endothelial cell
Anesthetic Implications in Stiff-Person Syndrome
Joel O. Johnson; Kirk A. Miller
1995-01-01
A 46-yr-old female presented to the operating room for repair of an intrathecal baclofen pump. Her diagnosis of SPS was based on clinical presentation and the presence of an autoantibody against the central nervous system enzyme glutamic acid decarboxylase (GAD). The syndrome began as muscle stiffness in her lower extremities and insidiously progressed to a state of constant stiffness resulting
Affine connections for the Cartesian stiffness matrix
Milos Zefran; Vijay Kumar
1997-01-01
We study the 6×6 Cartesian stiffness matrix. We show that the stiffness of a rigid body subjected to conservative forces and moments is described by a (0,2) tensor which is the Hessian of the potential function. The key observation of the paper is that since the Hessian depends on the choice of an affine connection in the task space, so
Concept for design of variable stiffness damper
NASA Technical Reports Server (NTRS)
Lohr, J. J.
1967-01-01
Damping mechanism, containing polymeric-like materials is applicable to a wide range of shock and vibration. The polymeric-like material changes from a relatively stiff material to a relatively soft, rubbery material in the region of their glass transition temperatures. The energy absorption characteristics and stiffness are controllable with temperature.
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.
Lakes, Roderic
Anomalies in stiffness and damping of a 2D discrete viscoelastic system due to negative stiffness containing a negative stiffness phase, anomalies in stiffness and damping have been observed experimentally Available online 24 February 2006 Abstract The recent development of using negative stiffness inclusions
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
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
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
Measuring the Characteristic Topography of Brain Stiffness with Magnetic Resonance Elastography
Murphy, Matthew C.; Huston, John; Jack, Clifford R.; Glaser, Kevin J.; Senjem, Matthew L.; Chen, Jun; Manduca, Armando; Felmlee, Joel P.; Ehman, Richard L.
2013-01-01
Purpose To develop a reliable magnetic resonance elastography (MRE)-based method for measuring regional brain stiffness. Methods First, simulation studies were used to demonstrate how stiffness measurements can be biased by changes in brain morphometry, such as those due to atrophy. Adaptive postprocessing methods were created that significantly reduce the spatial extent of edge artifacts and eliminate atrophy-related bias. Second, a pipeline for regional brain stiffness measurement was developed and evaluated for test-retest reliability in 10 healthy control subjects. Results This technique indicates high test-retest repeatability with a typical coefficient of variation of less than 1% for global brain stiffness and less than 2% for the lobes of the brain and the cerebellum. Furthermore, this study reveals that the brain possesses a characteristic topography of mechanical properties, and also that lobar stiffness measurements tend to correlate with one another within an individual. Conclusion The methods presented in this work are resistant to noise- and edge-related biases that are common in the field of brain MRE, demonstrate high test-retest reliability, and provide independent regional stiffness measurements. This pipeline will allow future investigations to measure changes to the brain’s mechanical properties and how they relate to the characteristic topographies that are typical of many neurologic diseases. PMID:24312570
Identification of Force Coefficients in Two Squeeze Film Dampers with a Central Groove
Seshagiri, Sanjeev
2012-07-16
frequency range to generate rectilinear, circular and elliptical orbits with specified motion amplitudes. A frequency domain method identifies the SFD mechanical parameters, viz., stiffness, damping, and added mass coefficients. The long damper generates...
Balantrapu, Achuta Kishore Rama Krishna
2005-11-01
Rotor-bearing system characteristics, such as natural frequencies, mode shapes, stiffness and damping coefficients, are essential to diagnose and correct vibration problems during system operation. Of the above characteristics, accurate...
STIFFNESS MODELING OF ROBOTIC-MANIPULATORS UNDER AUXILIARY LOADINGS
Paris-Sud XI, Université de
1 STIFFNESS MODELING OF ROBOTIC-MANIPULATORS UNDER AUXILIARY LOADINGS Alexandr Klimchik a and external loadings. It also produces the Cartesian stiffness matrix. This allows to extend the classical, France KEYWORDS Stiffness analysis, passive joints, auxiliary loading, static equilibrium, non
Design Optimization of Robot Manipulators over Global Stiffness Performance Evaluation
Paris-Sud XI, Université de
Design Optimization of Robot Manipulators over Global Stiffness Performance Evaluation Eric for the design optimization of robot manipulators with respect to multiple global stiffness objectives of our work resides : · in a systematic analytical calculation of the equivalent stiffness matrix
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-Poincaré 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.
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
Pseudo analytical solution to time periodic stiffness systems
NASA Astrophysics Data System (ADS)
Wang, Yan-Zhong; Zhou, Yuan-Zi
2011-04-01
An analytical form of state transition matrix for a system of equations with time periodic stiffness is derived in order to solve the free response and also allow for the determination of system stability and bifurcation. A pseudo-closed form complete solution for parametrically excited systems subjected to inhomogeneous generalized forcing is developed, based on the Fourier expansion of periodic matrices and the substitution of matrix exponential terms via Lagrange—Sylvester theorem. A Mathieu type of equation with large amplitude is presented to demonstrate the method of formulating state transition matrix and Floquet multipliers. A two-degree-of-freedom system with irregular time periodic stiffness characterized by spiral bevel gear mesh vibration is presented to find forced response in stability and instability. The obtained results are presented and discussed.
log(Tissue Stiffness) Development time
Discher, Dennis
of proteins, namely collagen plus cardiac- specific excitation-contraction proteins. Rapid softening-Contraction and Collagen Proteins, whereas Brain Remains SoHeartBeat log(Tissue Stiffness) Development time Excitation-Contraction Collagen #12;Current
Stiffness matrices of carbon nanotube structures
Samaroo, Kirk J. (Kirk Jerome)
2005-01-01
An analytical modeling study was done to determine the stiffness matrices of the lattice structure of graphene, the planar building block of carbon nanotubes. Through continuum linear elastic analysis and a displacement-based ...
OroSTIFF: Face-referenced measurement of perioral stiffness in health and disease
Chu, Shin-Ying; Kieweg, Douglas; Lee, Jaehoon
2010-01-01
A new device and automated measurement technology known as OroSTIFF is described to characterize non-participatory perioral stiffness in healthy adults for eventual application to patients with orofacial movement disorders associated with neuromotor disease, traumatic injury, or congenital clefts of the upper lip. Previous studies of perioral biomechanics required head stabilization for extended periods of time during measurement which precluded sampling patients with involuntary body/head movements (dyskinesias), or pediatric subjects. The OroSTIFF device is face-referenced and avoids the complications associated with head-restraint. Supporting data of non-participatory perioral tissue stiffness using OroSTIFF are included from 10 male and 10 female healthy subjects. The OroSTIFF device incorporates a pneumatic glass air cylinder actuator instrumented for pressure, and an integrated subminiature displacement sensor to encode lip aperture. Perioral electromyograms were simultaneously sampled to confirm passive muscle state for the superior and inferior divisions of the orbicularis oris muscles. Perioral stiffness, derived as a quotient from resultant force (?F) and interangle span (?X), was modeled with multilevel regression techniques. Real-time calculation of the perioral stiffness function demonstrated a significant quadratic relation between imposed interangle stretch and resultant force. This stiffness growth function also differed significantly between males and females. This study demonstrates the OroSTIFF ‘proof-of-concept’ for cost-effective non-invasive stimulus generation and derivation of perioral stiffness in a group of healthy unrestrained adults, and a case study to illustrate the dose-dependent effects of Levodopa on perioral stiffness in an individual with advanced Parkinson’s disease who exhibited marked dyskinesia and rigidity. PMID:20185131
Stiffness analysis of the humanoid robot WABIAN-RIV: modelling
Giuseppe Carbone; Hun-ok Limz; Atsuo Takanishi; Marco Ceccarelli
2003-01-01
In this paper a humanoid robot named as WABIAN-RIV (WAseda BIpedal humANoid Refined IV) is analyzed in terms of stiffness characteristics. This paper proposes basic models and a formulation in order to deduce the stiffness matrix as a function of the most important stiffness parameters of the WABIAN architecture. The proposed formulation is useful for numerical estimation of stiffness performances.
On the Normal Form of a Spatial Stiffness Matrix
Rodney G. Roberts
2002-01-01
A key result in the study of spatial stiffness matrices is Loncaric's normal form. When a spatial stiffness matrix is described in an appropriate coordinate frame, it will have a particularly simple structure. In this form, the 3×3 off-diagonal blocks of the stiffness matrix are diagonal. It has been shown that generically, a spatial stiffness matrix can be written in
On the problem of determination of spring stiffness parameters for
Tokyo, University of
into the conventional spring mesh model. Keywords. Mass-spring system, Finite element method, Stiffness matrix stiffness parameters by way of minimization of the matrix norm of the stiffness matrix of a triangle meshOn the problem of determination of spring stiffness parameters for spring-mesh models Huynh QUANG
Stiffness Estimation and Nonlinear Control of Robots with Variable Stiffness Actuation
De Luca, Alessandro
of estimating on line the nonlinear stiffness of flexible transmissions in robots with variable stiffness motion, the flexible transmission should behave in a nonlinear way. This can be obtained either through independent motors are used at each joint and motion is transmitted through nonlinear flexible transmissions
Constraint-based equilibrium and stiffness control of variable stiffness actuators
Matthew Howard; David J. Braun; Sethu Vijayakumar
2011-01-01
Considerable research effort has gone into the design of variable passive stiffness actuators (VSAs). A number of different mechanical designs have been proposed, aimed at either a biomorphic (i.e., antagonistic) design, compactness, or simplified modelling and control. In this paper, we propose a (model-based) unified control methodology that is able to exploit the benefits of variable stiffness independent of the
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.
Stiffness-weighted magnetic resonance imaging.
Glaser, Kevin J; Felmlee, Joel P; Manduca, Armando; Kannan Mariappan, Yogesh; Ehman, Richard L
2006-01-01
An imaging method is introduced in which the signal in MR images is affected by the stiffness distribution in the object being imaged. Intravoxel phase dispersion (IVPD) that occurs during MR elastography (MRE) acquisitions decreases the signal in soft regions more than in stiff regions due to changes in shear wave amplitude and wavelength. The IVPD effect is enhanced by lowpass filtering the MR k-space data with a circular Gaussian lowpass filter. A processing method is introduced to take the time series of MRE magnitude images with IVPD and produce a final stiffness-weighted image (SWI) by calculating the minimum signal at each pixel from a small number of temporal samples. The SWI technique is demonstrated in phantom studies as well as in the case of a preserved postmortem breast tissue specimen with a stiff lesion created by focused ultrasound ablation to mimic a breast cancer. When free of significant sources of depth-dependent wave attenuation, interference, and boundary effects, SWI is a simple, fast, qualitative technique that does not require the use of phase unwrapping or inversion algorithms for localizing stiff regions in an object. PMID:16342158
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
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
Al-Ghasem, Adnan Mahmoud
2005-08-29
] .......................................................................................2 Figure 3. Main test section of the test rig .....................................................................................9 Figure 4. Shaker-stinger configuration (NDE side.... Non-dimensional stiffness coefficients versus Sommerfeld number: (a) direct, and (b) cross-coupled..........................................................................................................59 Figure 45. Non...
Rotordynamic coefficients for a load-between-pad, flexible-pivot tilting pad bearing at high loads
Hensley, John Eric
2006-10-30
function of excitation frequency and curve fitted via linear regression to give the rotordynamic coefficients. The primary objectives were to determine whether the real component of the complex dynamic stiffnesses could be better modeled with or without...
Elastic Stiffness of a Skyrmion Crystal
NASA Astrophysics Data System (ADS)
Nii, Y.; Kikkawa, A.; Taguchi, Y.; Tokura, Y.; Iwasa, Y.
2014-12-01
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.
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.
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…
Substrate stiffness regulates cellular uptake of nanoparticles.
Huang, Changjin; Butler, Peter J; Tong, Sheng; Muddana, Hari S; Bao, Gang; Zhang, Sulin
2013-04-10
Nanoparticle (NP)-bioconjugates hold great promise for more sensitive disease diagnosis and more effective anticancer drug delivery compared with existing approaches. A critical aspect in both applications is cellular internalization of NPs, which is influenced by NP properties and cell surface mechanics. Despite considerable progress in optimization of the NP-bioconjugates for improved targeting, the role of substrate stiffness on cellular uptake has not been investigated. Using polyacrylamide (PA) hydrogels as model substrates with tunable stiffness, we quantified the relationship between substrate stiffness and cellular uptake of fluorescent NPs by bovine aortic endothelial cells (BAECs). We found that a stiffer substrate results in a higher total cellular uptake on a per cell basis, but a lower uptake per unit membrane area. To obtain a mechanistic understanding of the cellular uptake behavior, we developed a thermodynamic model that predicts that membrane spreading area and cell membrane tension are two key factors controlling cellular uptake of NPs, both of which are modulated by substrate stiffness. Our experimental and modeling results not only open up new avenues for engineering NP-based cancer cell targets for more effective in vivo delivery but also contribute an example of how the physical environment dictates cellular behavior and function. PMID:23484640
Biaxial strain and variable stiffness in aponeuroses
Azizi, Emanuel; Roberts, Thomas J
2009-01-01
The elastic structures of many muscles include both an extramuscular free tendon as well as a sheet-like aponeurosis. An important distinguishing feature of aponeuroses is that these tendinous structures function as the attachment and insertion surfaces of muscle fascicles and therefore surround a substantial portion of the muscle belly. As a result, aponeuroses must expand both parallel (longitudinal) and perpendicular (transverse) to a muscle's line of action when contracting muscles bulge to maintain a constant volume. In this study, we use biplanar high-speed fluoroscopy to track the strain patterns of the turkey lateral gastrocnemius aponeurosis during active and passive force production in situ. We find that the behaviour of the aponeurosis during passive force production is consistent with uniaxial loading, as aponeuroses stretch only in the longitudinal direction. By contrast, our results show that aponeuroses are stretched in both longitudinal and transverse directions during active force production and that transverse strains are on average 4 times greater than longitudinal strains. Biaxial loading of aponeuroses appears to effectively modulate longitudinal stiffness, as we find the measured stiffness in the longitudinal direction varies in proportion to transverse strain. We conclude that biaxial strain during active force production distinguishes aponeuroses from free tendons and may function to dynamically modulate stiffness along the axis of muscle force production. It is likely that consideration of strains measured only in the longitudinal direction result in an underestimation of aponeurosis stiffness as well as its capacity for elastic energy storage. PMID:19596897
On the numerical solution of stiff systems
Nuran Guzel; Mustafa Bayram
2005-01-01
In this paper, we use power series method to solve stiff ordinary differential equations of the first order and an ordinary differential equation of any order by converting it into a system of differential of the order one. Theoretical considerations has been discussed and some examples were presented to show the ability of the method for linear and nonlinear systems
Exploiting Variable Stiffness in Explosive Movement Tasks
Vijayakumar, Sethu
Exploiting Variable Stiffness in Explosive Movement Tasks David J. Braun, Matthew Howard and Sethu actuation is advantageous to robot control once high-performance, explosive tasks, such as throwing, hitting highly dynamic, explosive movements. Such movements are characterised by a large release of energy over
[Anaesthetic management of Stiff Man syndrome].
Marín, T; Hernando, D; Kinast, N; Churruca, I; Sabate, S
2015-04-01
Stiff Man syndrome or stiff-person syndrome is a rare autoimmune disorder. It is characterized by increased axial muscular tone and limb musculature, and painful spasms triggered by stimulus. The case is presented of a 44-year-old man with stiff-person syndrome undergoing an injection of botulinum toxin in the urethral sphincter under sedation. Before induction, all the surgical team were ready in order to minimise the anaesthetic time. The patient was monitored by continuous ECG, SpO2 and non-invasive blood pressure. He was induced with fractional dose of propofol 150 mg, fentanyl 50 ?g and midazolam 1mg. Despite careful titration, the patient had an O2 saturation level of 90%,which was resolved by manual ventilation. There was no muscle rigidity or spasm during the operation. Post-operative recovery was uneventful and the patient was discharged 2 days later. A review of other cases is presented. The anaesthetic concern in patients with stiff-person syndrome is the interaction between the anaesthetic agents, the preoperative medication, and the GABA system. For a safe anaesthetic management, total intravenous anaesthesia is recommended instead of inhalation anaesthetics, as well as the close monitoring of the respiratory function and the application of the electrical nerve stimulator when neuromuscular blockers are used. PMID:25060949
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
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
Cha, Gene
2013-11-07
systems and structures. The material comprises three constituents: negative springs, positive springs, and damping elements. These components help achieve high stiffness with passive adaptive response over a frequency range. When applying sinusoidal loads...
Design and characterization of tunable stiffness flexural bearings
Ramirez, Aaron Eduardo
2012-01-01
Compressed flexures have a downwards-tunable stiffness in their compliant directions; their stiffness can theoretically be reduced by up to four orders of magnitude. The compression-stiffiness relation is linear for most ...
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
Stiffness analysis and experimental validation of robotic systems
NASA Astrophysics Data System (ADS)
Carbone, Giuseppe
2011-06-01
Stiffness can be considered of primary importance in order to guarantee the successful use of any robotic system for a given task. Therefore, this paper proposes procedures for carrying out both numerical and experimental estimations of stiffness performance for multibody robotic systems. The proposed numerical procedure is based on models with lumped parameters for deriving the Cartesian stiffness matrix. Stiffness performance indices are also proposed for comparing stiffness performance. Then, an experimental procedure for the evaluation stiffness performance is proposed as based on a new measuring system named as Milli-CATRASYS (Milli Cassino Tracking System) and on a trilateration technique. Cases of study are reported to show the soundness and engineering feasibility of both the proposed numerical formulation for stiffness analysis and experimental validation of stiffness performance.
Kubo, Keitaro; Morimoto, Masanori; Komuro, Teruaki; Tsunoda, Naoya; Kanehisa, Hiroaki; Fukunaga, Tetsuo
2007-02-01
The present study aimed to examine the influences of tendon stiffness, joint stiffness, and electromyographic activity on jump performances consisting of a single-joint movement. Twenty-four men performed three kinds of unilateral maximal jump using only the ankle joint (squat jump: SJ; countermovement jump: CMJ; drop jump: DJ) on the sledge apparatus. The relative differences in the jump height of CMJ and DJ compared to SJ were defined as pre-stretch augmentation. During jumping exercises, electromyographic activities (mEMG) were recorded from the plantar flexors. Ankle joint stiffness was calculated as the change in the joint torque divided by the change in ankle joint angle during the eccentric phase of DJ. Achilles tendon stiffness was measured using ultrasonography during isometric plantar flexion. No significant correlations were found between joint stiffness and pre-stretch augmentation in both CMJ and DJ. On the contrary, tendon stiffness was significantly correlated with pre-stretch augmentation in both CMJ (r = -0.471) and DJ (r = -0.502). The relative mEMG value of CMJ (to that of SJ) during the concentric phase was significantly correlated with pre-stretch augmentation (r = 0.481), although this relationship was not found in DJ. These results suggested that (1) the greater jump height in CMJ could be explained by both the tendon elasticity and the increased activation level of muscle, (2) tendon elasticity played a more significant role in the enhancement of jump height during DJ, and (3) joint stiffness was not related to either pre-stretch augmentation or tendon stiffness. PMID:17106717
Keitaro Kubo; Masanori Morimoto; Teruaki Komuro; Naoya Tsunoda; Hiroaki Kanehisa; Tetsuo Fukunaga
2007-01-01
The present study aimed to examine the influences of tendon stiffness, joint stiffness, and electromyographic activity on\\u000a jump performances consisting of a single-joint movement. Twenty-four men performed three kinds of unilateral maximal jump\\u000a using only the ankle joint (squat jump: SJ; countermovement jump: CMJ; drop jump: DJ) on the sledge apparatus. The relative\\u000a differences in the jump height of CMJ
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 (R(2)?=?92%) and flexion portions (R(2)?=?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
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
Control of seismic-excited buildings using active variable stiffness systems
J. N. Yang; Z. Li; J. C. Wu
1994-01-01
Active variable stiffness (AVS) systems have been demonstrated to be effective in response control of buildings subjected to earthquake excitations. Based on the theory of variable structure system (VSS) or sliding mode control (SMC), control methods for applications of AVS systems to seismic-excited buildings are presented. In addition to full-state feedback controllers, general static output feedback controllers as well as
Christoph D. Gatzka; James D. Cameron; Bronwyn A. Kingwell; Anthony M. Dart
To elucidate the relationship between coronary artery disease (CAD), aortic stiffness, and left ventricular structure, we recruited 55 subjects (33 men; average age, 6361 years) with previously unknown CAD from a healthy general population sample, as well as 55 control subjects matched for gender, age, and serum cholesterol level. We measured arterial blood pressure and the systolic expansion of the
Stiffness Properties Of Laminated Graphite/Epoxy Cylinders
NASA Technical Reports Server (NTRS)
Tolbert, R. Noel
1988-01-01
Report discusses stiffnesses of cylindrical shells formed from composite graphite/epoxy laminates, as calculated from traditional composite-lamination theory. Shells evaluated for use as cases for solid-fuel rocket motors. Stiffness results compared with quasi-experimental stiffnesses developed from pressure tests of cylindrical bottles. Sensitivities of stiffnesses to variations in constituent materials and in geometric parameters examined with help of two computer programs, included in appendix to report.
Stiffness analysis and experimental validation of robotic systems
Giuseppe Carbone
2011-01-01
Stiffness can be considered of primary importance in order to guarantee the successful use of any robotic system for a given\\u000a task. Therefore, this paper proposes procedures for carrying out both numerical and experimental estimations of stiffness\\u000a performance for multibody robotic systems. The proposed numerical procedure is based on models with lumped parameters for\\u000a deriving the Cartesian stiffness matrix. Stiffness
The passive stiffness of the wrist and forearm.
Formica, Domenico; Charles, Steven K; Zollo, Loredana; Guglielmelli, Eugenio; Hogan, Neville; Krebs, Hermano I
2012-08-01
Because wrist rotation dynamics are dominated by stiffness (Charles SK, Hogan N. J Biomech 44: 614-621, 2011), understanding how humans plan and execute coordinated wrist rotations requires knowledge of the stiffness characteristics of the wrist joint. In the past, the passive stiffness of the wrist joint has been measured in 1 degree of freedom (DOF). Although these 1-DOF measurements inform us of the dynamics the neuromuscular system must overcome to rotate the wrist in pure flexion-extension (FE) or pure radial-ulnar deviation (RUD), the wrist rarely rotates in pure FE or RUD. Instead, understanding natural wrist rotations requires knowledge of wrist stiffness in combinations of FE and RUD. The purpose of this report is to present measurements of passive wrist stiffness throughout the space spanned by FE and RUD. Using a rehabilitation robot designed for the wrist and forearm, we measured the passive stiffness of the wrist joint in 10 subjects in FE, RUD, and combinations. For comparison, we measured the passive stiffness of the forearm (in pronation-supination), as well. Our measurements in pure FE and RUD agreed well with previous 1-DOF measurements. We have linearized the 2-DOF stiffness measurements and present them in the form of stiffness ellipses and as stiffness matrices useful for modeling wrist rotation dynamics. We found that passive wrist stiffness was anisotropic, with greater stiffness in RUD than in FE. We also found that passive wrist stiffness did not align with the anatomical axes of the wrist; the major and minor axes of the stiffness ellipse were rotated with respect to the FE and RUD axes by ?20°. The direction of least stiffness was between ulnar flexion and radial extension, a direction used in many natural movements (known as the "dart-thrower's motion"), suggesting that the nervous system may take advantage of the direction of least stiffness for common wrist rotations. PMID:22649208
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.
Accuracy of an approximate static structural analysis technique based on stiffness matrix eigenmodes
NASA Technical Reports Server (NTRS)
Sobieszczanski-Sobieski, J.; Hajela, P.
1979-01-01
Use of the stiffness matrix eigenmodes, instead of the vibration eigenmodes, as generalized coordinates is proposed for condensation of static load deflection equations in finite element stiffness method. The modes are selected by strain energy criteria and the resulting fast, approximate analysis technique is evaluated by applications to idealized built-up wings and a fuselage segment. The best results obtained are a two-order of magnitude reduction of the number of degrees of freedom in a high aspect ratio wing associated with less than one percent error in prediction of the largest displacement.
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.
Elastic stars in general relativity: III. Stiff ultrarigid exact solutions
NASA Astrophysics Data System (ADS)
Karlovini, Max; Samuelsson, Lars
2004-10-01
We present an equation of state for elastic matter which allows for purely longitudinal elastic waves in all propagation directions, not just principal directions. The speed of these waves is equal to the speed of light whereas the transversal type speeds are also very high, comparable to but always strictly less than that of light. Clearly such an equation of state does not give a reasonable matter description for the crust of a neutron star, but it does provide a nice causal toy model for an extremely rigid phase in a neutron star core, should such a phase exist. Another reason for focusing on this particular equation of state is simply that it leads to a very simple recipe for finding stationary rigid motion exact solutions to the Einstein equations. In fact, we show that a very large class of stationary spacetimes with constant Ricci scalar can be interpreted as rigid motion solutions with this matter source. We use the recipe to derive a static spherically symmetric exact solution with constant energy density, regular centre and finite radius, having a nontrivial parameter that can be varied to yield a mass radius curve from which stability can be read off. It turns out that the solution is stable down to a tenuity R/M slightly less than 3. The result of this static approach to stability is confirmed by a numerical determination of the fundamental radial oscillation mode frequency. We also present another solution with outwards decreasing energy density. Unfortunately, this solution only has a trivial scaling parameter and is found to be unstable.
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
Haptic Identification of Stiffness and Force Magnitude Steven A. Cholewiak,
Tan, Hong Z.
Haptic Identification of Stiffness and Force Magnitude Steven A. Cholewiak, 1 Hong Z. Tan, 1 investigated the channel capacity for transmitting information through stiffness or force magnitude. Specifically, we measured the number of stiffness or force- magnitude levels that can be reliably identified
Active stiffness control of a manipulator in cartesian coordinates
J. Kenneth Salisbury
1980-01-01
A method of actively controlling the apparent stiffness of a manipulator end effecter is presented. The approach allows the programmer to specify the three transnational and three rotational stiffness of a frame located arbitrarily in hand coordinates. Control of the nominal position of the hand then permits simultaneous position and force control. Stiffness may be changed under program control to
The geometric stiffness of triangular composite-materials shell elements
E. Gal; R. Levy
2005-01-01
This paper is concerned with the development of the geometric stiffness matrix for Newton type large rotation analysis of composite thin shell structures. The geometric stiffness matrix is derived from load perturbation of the discrete equilibrium equations of a given linear finite element formulation. The geometric stiffness matrix is extracted from the gradient, in global coordinates, of the element nodal
A Modified Face Seal For Positive Film Stiffness
A. Lipshitz; I. Etsion
1978-01-01
A modified face seal having a positive film stiffness is described and analyzed. The axial film stiffness is obtained by simply extending the seal nosepiece towards the shaft, thereby producing an annular clearance seal in series with the original face seal.Conditions for maximum film stiffness and pressure balance operation of the modified seal are derived. A comparison is made between
Static stiffness modeling of a novel hybrid redundant robot machine
Ming Li; Huapeng Wu; Heikki Handroos
2011-01-01
This paper presents a modeling method to study the stiffness of a hybrid serial–parallel robot IWR (Intersector Welding Robot) for the assembly of ITER vacuum vessel. The stiffness matrix of the basic element in the robot is evaluated using matrix structural analysis (MSA); the stiffness of the parallel mechanism is investigated by taking account of the deformations of both hydraulic
STIFFNESS SYNTHESIS OF A VARIABLE GEOMETRY PLANAR ROBOT
Simaan, Nabil
STIFFNESS SYNTHESIS OF A VARIABLE GEOMETRY PLANAR ROBOT Nabil Simaan and Moshe Shoham Robotics, in which, three parameters of the stiffness matrix are controlled according to task requirements robot, Re-configurable, Stiffness Synthesis, Gröbner bases. 1. Introduction Robots are used to perform
Stiffness Analysis Of Multi-Chain Parallel Robotic Systems
Anatoly Pashkevich; Damien Chablat; Philippe Wenger
2008-01-01
The paper presents a new stiffness modelling method for multi-chain parallel robotic manipulators with flexible links and compliant actuating joints. In contrast to other works, the method involves a FEA-based link stiffness evaluation and employs a new solution strategy of the kinetostatic equations, which allows computing the stiffness matrix for singular postures and to take into account influence of the
Stiffness Modeling for an Orthogonal 3-PUU Compliant Parallel Micromanipulator
Li, Yangmin
Stiffness Modeling for an Orthogonal 3-PUU Compliant Parallel Micromanipulator Qingsong Xu-- The stiffness modeling for a compliant parallel manipulator (CPM) is very important since it provides a basis compliant element, the analytical stiffness model for a spatial CPM is established by a straightforward
Stiffness Modeling of a Spatial 3-DOF Compliant Parallel Micromanipulator
Li, Yangmin
Stiffness Modeling of a Spatial 3-DOF Compliant Parallel Micromanipulator Qingsong Xu and Yangmin@umac.mo Abstract-- The stiffness modeling for a compliant parallel manipulator (CPM) is very important since the compliance of each compliant element, which is then applied to stiffness modeling of the 3-PRC CPM
STIFFNESS MAPPING OF PLANAR COMPLIANT PARALLEL MECHANISMS IN A
Florida, University of
STIFFNESS MAPPING OF PLANAR COMPLIANT PARALLEL MECHANISMS IN A SERIAL ARRANGEMENT Hyun K. Jung of a mechanism having two planar compliant parallel mechanisms in a serial arrangement. The stiffness matrix of the mechanism. A numerical example is presented. Keywords: Stiffness matrix, compliant coupling, parallel
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 10 min). The sliced yam were soaked in water for 12 h, 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 2.92 ml H2O/g and 0.71 to 0.88 g/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
Boyer, Edmond
Stiffness matrix of manipulators with passive joints: computational aspects 1 Abstract--The paper focuses on stiffness matrix computation for manipulators with passive joints, compliant actuators of a robotic system. To evaluate stiffness properties, several methods can be applied such as Finite Element
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.
METHOD OF HYPERBOLIC SYSTEMS WITH STIFF RELAXATION
R. B. LOWRIE; J. E. MOREL
2001-03-01
Three methods are analyzed for solving a linear hyperbolic system that contains stiff relaxation. We show that the semi-discrete discontinuous Galerkin method, with a linear basis, is accurate when the relaxation time is unresolved (asymptotically preserving--AP). A recently developed central method is shown to be non-AP. To discriminate between AP and non-AP methods, we argue that one must study problems that are diffusion dominated.
Lipedema is associated with increased aortic stiffness.
Szolnoky, G; Nemes, A; Gavallér, H; Forster, T; Kemény, L
2012-06-01
Lipedema is a disproportional obesity due to unknown pathomechanism. Its major hallmark is frequent hematoma formation related to increased capillary fragility and reduced venoarterial reflex. Beyond microangiopathy, both venous and lymphatic dysfunction have also been documented. However, arterial circulation in lipedema has not been examined, and therefore we explored aortic elastic properties by echocardiography. Fourteen women with and 14 without lipedema were included in the study. Each subject consented to blood pressure measurement, physical examination, and transthoracic echocardiography. Aortic stiffness index (beta), distensibility, and strain were evaluated from aortic diameter and blood pressure data. Mean systolic (30.0 +/- 3.2 vs. 25.5 +/- 3.6, P < 0.05) and diastolic (27.8 +/- 3.3 vs. 22.3 +/- 3.1) aortic diameters (in mm) and aortic stiffness index (9.05 +/- 7.45 vs. 3.76 +/- 1.22, P < 0.05) were significantly higher, while aortic strain (0.082 +/- 0.04 vs. 0.143 +/- 0.038, P < 0.05) and distensibility (2.24 +/- 1.07 vs. 4.38 +/- 1.61, P < 0.05) were significantly lower in lipedematous patients compared to controls. Thus, lipedema is characterized with increased aortic stiffness. PMID:23057152
Main, Russell P.; Lynch, Maureen E.; van der Meulen, Marjolein C.H.
2010-01-01
Whole bone morphology, cortical geometry, and tissue material properties modulate skeletal stresses and strains that in turn influence skeletal physiology and remodeling. Understanding how bone stiffness, the relationship between applied load and tissue strain, is regulated by developmental changes in bone structure and tissue material properties is important in implementing biophysical strategies for promoting healthy bone growth and preventing bone loss. The goal of this study was to relate developmental patterns of in vivo whole bone stiffness to whole bone morphology, cross-sectional geometry, and tissue properties using a mouse axial loading model. We measured in vivo tibial stiffness in three age groups (6wks, 10wks, 16wks old) of female C57Bl/6 mice during cyclic tibial compression. Tibial stiffness was then related to cortical geometry, longitudinal bone curvature, and tissue mineral density using microcomputed tomography (microCT). Tibial stiffness and the stresses induced by axial compression were generally maintained from 6 to 16wks of age. Growth-related increases in cortical cross-sectional geometry and longitudinal bone curvature had counteracting effects on induced bone stresses and, therefore, maintained tibial stiffness similarly with growth. Tissue mineral density increased slightly from 6 to 16wks of age, and although the effects of this increase on tibial stiffness were not directly measured, its role in the modulation of whole bone stiffness was likely minor over the age range examined. Thus, whole bone morphology, as characterized by longitudinal curvature, along with cortical geometry, plays an important role in modulating bone stiffness during development and should be considered when evaluating and designing in vivo loading studies and biophysical skeletal therapies. PMID:20673665
Nonlinear effects on the stiffness of bolted joints
Lehnhoff, T.F. [Univ. of Missouri, Rolla, MO (United States). Dept. of Mechanical and Aerospace Engineering; Wistehuff, W.E. [General Motors Corp., Pontiac, MI (United States)
1996-02-01
Axisymmetric finite element modeling of bolted joints was performed to show the effects of the magnitude and position of the external load, member thickness, and member material on the bolt and member stiffnesses. The member stiffness of the bolted joint was found to decrease 10 to 42 percent for the 20-mm to 8-mm bolts, respectively, as the magnitude of the external load was increased. Member stiffness appears to be independent of the radial location of the external load and increases as the member thickness decreases. Member stiffness decreased by a factor of 2.5 to 3 with a change in the member material from steel to aluminum. The cast iron members had a decrease in member stiffness of a factor of 1.7 to 1.9. The aluminum over cast iron combination had a member stiffness between the aluminum and cast iron alone. Bolt stiffnesses varied by less than two percent for changes in the magnitude of the external load for all bolt sizes and member materials, except for the 8-mm bolt where stiffness increased by approximately 11 percent. Changes in radial position of the external load had no effect on the bolt stiffness. A 3 to 13-percent decrease in the bolt stiffness was found when changing from steel to aluminum members. A 2 to 3-percent bolt stiffness decrease resulted when the member material was changed from steel to cast iron and similarly from steel to the aluminum over cast iron combination.
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, 147–180, to make measurements on the stiffness of the human lens. These new procedures have been developed in an attempt to eliminate, or at least substantially reduce, various systematic errors in Fisher’s original experiment. An improved test rig has been constructed and a new modelling procedure for determining lens stiffness parameters from observations made during the test has been devised. The experiment involves mounting a human lens on a vertical rotor so that the lens spins on its optical axis (typically at 1000 rpm). An automatic imaging system is used to capture the outline of the lens, while it is rotating, at pre-determined angular orientations. These images are used to quantify the deformations developed in the lens as a consequence of the centripetal forces induced by the rotation. Lens stiffness is inferred using axisymmetric finite element inverse analysis in which a nearly-incompressible neo-Hookean constitutive model is used to represent the mechanics of the lens. A numerical optimisation procedure is used to determine the stiffness parameters that provide a best fit between the finite element model and the experimental data. Sample results are presented for a human lens of age 33 years. PMID:21040722
Muscle short-range stiffness can be used to estimate the endpoint stiffness of the human arm
Hu, Xiao; Murray, Wendy M.
2011-01-01
The mechanical properties of the human arm are regulated to maintain stability across many tasks. The static mechanics of the arm can be characterized by estimates of endpoint stiffness, considered especially relevant for the maintenance of posture. At a fixed posture, endpoint stiffness can be regulated by changes in muscle activation, but which activation-dependent muscle properties contribute to this global measure of limb mechanics remains unclear. We evaluated the role of muscle properties in the regulation of endpoint stiffness by incorporating scalable models of muscle stiffness into a three-dimensional musculoskeletal model of the human arm. Two classes of muscle models were tested: one characterizing short-range stiffness and two estimating stiffness from the slope of the force-length curve. All models were compared with previously collected experimental data describing how endpoint stiffness varies with changes in voluntary force. Importantly, muscle properties were not fit to the experimental data but scaled only by the geometry of individual muscles in the model. We found that force-dependent variations in endpoint stiffness were accurately described by the short-range stiffness of active arm muscles. Over the wide range of evaluated arm postures and voluntary forces, the musculoskeletal model incorporating short-range stiffness accounted for 98 ± 2, 91 ± 4, and 82 ± 12% of the variance in stiffness orientation, shape, and area, respectively, across all simulated subjects. In contrast, estimates based on muscle force-length curves were less accurate in all measures, especially stiffness area. These results suggest that muscle short-range stiffness is a major contributor to endpoint stiffness of the human arm. Furthermore, the developed model provides an important tool for assessing how the nervous system may regulate endpoint stiffness via changes in muscle activation. PMID:21289133
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.
Aortic stiffness and distensibility among hypertensives.
Meenakshisundaram, R; Kamaraj, K; Murugan, S; Thirumalaikolundusubramanian, P
2009-09-01
Hypertension is one among many factors that contribute to aortic stiffness, which has repercussions mainly on the heart. To assess aortic stiffness among essential hypertensives of South India and its relationship with gender. An analytical study was designed to assess aortic stiffness among 60 nonobese, nonalcoholic, nonsmoking, and non-caffeine consuming essential hypertensives without any overt illness or infection, and compared with 30 healthy age- and sex-matched nonhypertensives. They were assessed clinically and also by laboratory means. Their left ventricular mass (LV) and left ventricular ejection fraction (LVEF) were measured using Transthoracic echocardiogram. Aortic systolic and diastolic diameters were measured by using M-mode echocardiography during consecutive beats and averaged for each case. Finally, aortic stiffness was calculated. The data were analyzed statistically. Hypertensives were divided into Group I, consisting of patients with hypertension at least for 5 years, who were not adherent to medication, and Group II, consisting of patients with hypertension of duration between 6 months and 1 year. There were 20 males and 10 females in each group. There was no significant difference between the hypertensive groups and a control, normotensive, group with regard to BMI or total cholesterol. The means of LV mass (in grams), systolic BP (in mmHg), diastolic BP (in mmHg), aortic systolic diameter (in mm), aortic diastolic diameter (in mm), aortic distensibility (in mm), and aortic stiffness found in Group I, Group II, and controls were 105.8 +/- 23.8, 101.5 +/- 21, and 84 +/- 9.8; 138 +/- 14.2, 153 +/- 17.1, and 120 +/- 8.3; 90.5 +/- 11.6, 101.7 +/- 17.1, and 76.5 +/- 5; 30.85 +/- 2.6, 28.7 +/- 2.6, and 27.7 +/- 2.4; 28.7 +/- 2.2, 25.8 +/- 2.5, and 24.2 +/- 2.5; 2.14 +/- 0.3, 2.84 +/- 0.5, and 3.5 +/- 0.6; and 1.31 +/- 0.09, 1.14 +/- 0.1, and 1.04 +/- 0.08, respectively. The differences between the hypertensive groups and the control group were significant. Aortic stiffness was greater in hypertensives and it was independent of gender, but increased with duration of hypertension. Hypertension has effects on the aorta (decreased aortic distensibility and increased aortic stiffness) and left ventricle (increased left ventricular mass and left ventricular hypertrophy). These changes can be identified and monitored while the patient is on antihypertensive therapy along with life-style modifications, as these are reversible. Nevertheless, these aspects do not receive due attention in medical education and training on hypertension. PMID:19751418
Reduced pulmonary function is associated with central arterial stiffness in men.
Zureik, M; Benetos, A; Neukirch, C; Courbon, D; Bean, K; Thomas, F; Ducimetière, P
2001-12-15
The association of impaired pulmonary function with cardiovascular morbidity and mortality has been reported in several prospective studies. The nature of this association and the mechanisms underlying it are unknown. Both atherosclerosis and central arterial stiffness might be involved. We recently reported, in a 4-yr longitudinal study, that reduced lung function predicts the development of carotid atherosclerotic plaques. In the present study, we report the associations of aortic stiffness with lung function measurements. One hundred and ninety-four men, aged 30 to 70 yr and free of coronary heart disease, who volunteered for a standard health examination were included. FEV(1) and FVC were used to assess lung function. Aortic stiffness was estimated from the carotid-femoral pulse-wave velocity (PWV), which increases proportionally with an increase in aortic stiffness. PWV was significantly and negatively associated with FEV(1) and FVC (partial correlation coefficients adjusted for age and height: -0.27 [p < 0.001] and -0.24 [p < 0.001], respectively). For every 1 SD increase in PWV (2.5 m/s), FEV(1) decreased by 195.2 +/- 50.1 ml (p < 0.001) in an age- and height-adjusted analysis. The corresponding decrease in FVC was 190.4 +/- 55.0 ml (p < 0.001). Further adjustment for cardiovascular risk factors (weight, smoking habits, hypercholesterolemia, diabetes, and hypertension) did not markedly alter these results. In addition, negative associations of PWV with lung function measurements were observed within each category of cardiovascular risk factors. This study suggests that reduced pulmonary function is independently associated with aortic stiffness in men. The interrelations between pulmonary and vascular alterations should be thoroughly investigated. PMID:11751184
Friction and stem stiffness affect dynamic interface motion in total hip replacement.
Kuiper, J H; Huiskes, R
1996-01-01
Large cyclic movements between the femoral stem and bone during the first weeks after total hip arthroplasty may hamper bone ingrowth and adversely affect the eventual success of the arthroplasty. Little is known, however, about the magnitude of the motions and its relationship to design and surgical factors. A two-dimensional finite element model of a cementless prosthesis inserted into the proximal femur was constructed to study the effects of two mechanical variables--the stiffness of the implant and the coefficient of friction between bone and implant--on the magnitude of the motions. We investigated the influences of these variables on the subsidence of the prosthesis, the magnitudes of the cyclic motions, and the level of the interface stresses. The presence of friction reduced cyclic motions by about 85% compared with a frictionless interface. Once friction was assumed, varying the coefficient of friction had little effect. The effect of friction on the interface stress state and gross subsidence of the prosthesis was not as great as on cyclic motion. Implant stiffness also affected the magnitudes and distributions of the cyclic motions along the interface. A flexible stem generated motions about three to four times larger proximally than those of a stiff stem, which generated larger motions distally. The influence of stem stiffness on interface stresses and prosthetic subsidence was less than on cyclic motion. The location of the peak shear stresses at the interface around a bonded prosthesis corresponded to the location where cyclic interface motion was maximal for an unbonded prosthesis. However, no direct relationship was found between the magnitudes of peak stresses and the amplitudes of cyclic motions. PMID:8618164
Rodriguez Colmenares, Luis Emigdio
2004-09-30
This thesis provides experimental frequency dependent stiffness and damping coefficient results for a high-speed, lightly loaded, flexible-pivot tilting-pad bearing, with a load-on-pad configuration. Test conditions include four shaft speeds (6000...
Normal response function method for mass and stiffness matrix updating using complex FRFs
NASA Astrophysics Data System (ADS)
Pradhan, S.; Modak, S. V.
2012-10-01
Quite often a structural dynamic finite element model is required to be updated so as to accurately predict the dynamic characteristics like natural frequencies and the mode shapes. Since in many situations undamped natural frequencies and mode shapes need to be predicted, it has generally been the practice in these situations to seek updating of only mass and stiffness matrix so as to obtain a reliable prediction model. Updating using frequency response functions (FRFs) has been one of the widely used approaches for updating, including updating of mass and stiffness matrices. However, the problem with FRF based methods, for updating mass and stiffness matrices, is that these methods are based on use of complex FRFs. Use of complex FRFs to update mass and stiffness matrices is not theoretically correct as complex FRFs are not only affected by these two matrices but also by the damping matrix. Therefore, in situations where updating of only mass and stiffness matrices using FRFs is required, the use of complex FRFs based updating formulation is not fully justified and would lead to inaccurate updated models. This paper addresses this difficulty and proposes an improved FRF based finite element model updating procedure using the concept of normal FRFs. The proposed method is a modified version of the existing response function method that is based on the complex FRFs. The effectiveness of the proposed method is validated through a numerical study of a simple but representative beam structure. The effect of coordinate incompleteness and robustness of method under presence of noise is investigated. The results of updating obtained by the improved method are compared with the existing response function method. The performance of the two approaches is compared for cases of light, medium and heavily damped structures. It is found that the proposed improved method is effective in updating of mass and stiffness matrices in all the cases of complete and incomplete data and with all levels and types of damping.
The Multidimensional Random Coefficients Multinomial Logit Model
Raymond J. Adams; Mark Wilson; Wen-chung Wang
1997-01-01
A multidimensional Rasch-type item response model, the multidimensional random coefficients multinomial logit model, is presented as an extension to the Adams & Wilson (1996) random coefficients multinomial logit model. The model is developed in a form that permits generalization to the multidimensional case of a wide class of Rasch models, including the simple logistic model, Masters' partial credit model, Wilson's
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…
Driss, Tarak; Lambertz, Daniel; Rouis, Majdi; Vandewalle, Henry
2012-11-01
The importance of maximal voluntary torque (T (MVC)), maximal rate of torque development (MRTD) and musculo-tendinous stiffness of the triceps surae for maximal power output on a cycle ergometre (Pmax) was studied in 21 healthy subjects by studying the relationships between maximal cycling power related to body mass (Pmax BM(-1)) with T (MVC), MRTD and different indices of musculo-tendinous stiffness of the ankle flexor. Pmax BM(-1) was calculated from the data of an all-out force-velocity test on a Monark cycle ergometre. T (MVC) and MRTD were measured on a specific ankle ergometre. Musculo-tendinous stiffness was estimated by means of quick releases at 20, 40, 60 and 80% T (MVC) on the same ankle ergometre. Pmax BM(-1) was significantly and positively correlated with MRTD related to body mass but the positive correlation between Pmax BM(-1) and T (MVC) did not reach the significance level (0.05). Pmax BM(-1) was significantly and positively correlated with the estimation of stiffness at 40% T (MVC) (S(0.4)), but not with stiffness at 20, 60 and 80% T (MVC). The results of the present study suggest that maximal power output during cycling is significantly correlated with the level of musculo-tendinous stiffness which corresponds to torque range around peak torque at optimal pedal rate. However, the low coefficient of determination (r2 = 0.203) between Pmax BM(-1) and S (0.4) BM(-1) suggested that Pmax BM(-1) largely depended on other factors than the musculo-tendinous stiffness of the only plantar flexors. PMID:22354446
Relative stiffness of flat conductor cables
NASA Technical Reports Server (NTRS)
Hankins, J. D.
1976-01-01
The measurement of the bending moment required to obtain a given deflection in short lengths of flat conductor cable (FCC) is presented in this report. Experimental data were taken on 10 different samples of FCC and normalized to express all bending moments (relative stiffness factor) in terms of a cable 5.1 cm (2.0 in.) in width. Data are presented in tabular and graphical form for the covenience of designers who may be interested in finding torques exerted on critical components by short lengths of FCC.
Mathew James Dickson; Franz Konstantin Fuss; Kevin Gerard Wong
2010-01-01
Boccia is a Paralympic sport for athletes with cerebral palsy and certain other conditions, such as muscular dystrophy, that cause impairments similar to cerebral palsy. Boccia balls are either thrown or rolled down the court using an assistive device, i.e. a ramp. The balls are filled with plastic granules. The aim of this study was to characterise the balls based
Knowles, Kevin M.; Howie, Philip R.
2014-12-31
.: Elasticity and Anelasticity of Metals. University of Chicago Press, Chicago (1948) 18. Ledbetter, H., Moment, R.L.: Elastic properties of face-centered-cubic plutonium. Acta Metall. 24, 891– 899 (1976) 19. Bolef, D.I.: Elastic constants of single crystals...
Kiyomi Mori; Hiroaki Isono; Toshio Sugibayashi
1992-01-01
The effect of adherend stiffness on the joint strength is examined by varying the adherend material and varying aspect ratio of the adherend dimension. The joint type used in this study is a stepped-lap bonded joint. The joint materials are three kinds of metals, carbon steel, brass and aluminum alloy, for the adherends and an epoxy resin for the adhesive.
Advanced Glycation End-Products and Arterial Stiffness in Hypertension
Marie McNulty; Azra Mahmud; John Feely
2007-01-01
Background: The formation of advanced glycation end-products is associated with arterial stiffness in experimental models and alagebrium (formerly known as ALT-711), an advanced glycation end-product cross-link breaker, has been shown to reduce arterial stiffness in elderly subjects.Methods: We related plasma concentrations of advanced glycation end-products (AGEs), measured using a noncompetitive immunoassay, and markers of aortic stiffness—pulse wave velocity (PWV) and
Properties of the Grasp Stiffness Matrix and Conservative Control Strategies
Inmin Kao; Chi Ngo
1999-01-01
In this paper, we present fundamental properties of stiffness matrices as applied in analysis of grasping and dextrous manipulation in configuration spaces and linear Euclidean R3×3 space without rotational components. A conservative-stiffness matrix in such spaces needs to satisfy both symmetric and exact differential criteria. Two types of stiffness matrices are discussed: constant and configuration-dependent matrices. The symmetric part of
On the Stiffness and Stability of Gough-Stewart Platforms
Mikhail M. Svinin; Shigeyuki Hosoe; Masaru Uchiyama
2001-01-01
This paper deals with a class of parallel mechanisms, called Gough-Stewart platforms. For these mechanisms, pre-loaded by driving forces, the stiffness matrix is derived and its basic properties are established. It is shown when the stiffness matrix becomes asymmetric, how the parametric imbalance may influence the system stability, and how the center of stiffness depends on the force pre-loading. Next,
Properties of the grasp stiffness matrix and conservative control strategies
I. Kao; C. Ngo
1999-01-01
In this paper, the authors present fundamental properties of stiffness matrices as applied in analysis of grasping and dexterous manipulation in configuration spaces and linear Euclidean R{sup 3x3} space without rotational components. A conservative-stiffness matrix in such spaces needs to satisfy both symmetric and exact differential criteria. Two types of stiffness matrices are discussed: constant and configuration-dependent matrices are discussed:
Stiffness Analysis Of Multi-Chain Parallel Robotic Systems
Anatoly Pashkevich; Alexandr Klimchik; Damien Chablat; Philippe Wenger
2009-01-01
The paper presents a new stiffness modelling method for multi-chain parallel\\u000arobotic manipulators with flexible links and compliant actuating joints. In\\u000acontrast to other works, the method involves a FEA-based link stiffness\\u000aevaluation and employs a new solution strategy of the kinetostatic equations,\\u000awhich allows computing the stiffness matrix for singular postures and to take\\u000ainto account influence of the
Experiments on dynamic stiffness and damping of tapered bore seals
NASA Technical Reports Server (NTRS)
Fleming, D. 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.
A Stiffness Switch in Human Immunodeficiency Virus
Kol, Nitzan; Shi, Yu; Tsvitov, Marianna; Barlam, David; Shneck, Roni Z.; Kay, Michael S.; Rousso, Itay
2007-01-01
After budding from the cell, human immunodeficiency virus (HIV) and other retrovirus particles undergo a maturation process that is required for their infectivity. During maturation, HIV particles undergo a significant internal morphological reorganization, changing from a roughly spherically symmetric immature particle with a thick protein shell to a mature particle with a thin protein shell and conical core. However, the physical principles underlying viral particle production, maturation, and entry into cells remain poorly understood. Here, using nanoindentation experiments conducted by an atomic force microscope (AFM), we report the mechanical measurements of HIV particles. We find that immature particles are more than 14-fold stiffer than mature particles and that this large difference is primarily mediated by the HIV envelope cytoplasmic tail domain. Finite element simulation shows that for immature virions the average Young's modulus drops more than eightfold when the cytoplasmic tail domain is deleted (930 vs. 115 MPa). We also find a striking correlation between the softening of viruses during maturation and their ability to enter cells, providing the first evidence, to our knowledge, for a prominent role for virus mechanical properties in the infection process. These results show that HIV regulates its mechanical properties at different stages of its life cycle (i.e., stiff during viral budding versus soft during entry) and that this regulation may be important for efficient infectivity. Our report of this maturation-induced “stiffness switch” in HIV establishes the groundwork for mechanistic studies of how retroviral particles can regulate their mechanical properties to affect biological function. PMID:17158573
Factors influencing left-ventricular stiffness.
Yettram, A L; Grewal, B S; Dawson, J R; Gibson, D G
1992-01-01
The aim of the study was to investigate the relative contributions of geometrical and material factors to overall left-ventricular cavity stiffness. Left-ventricular cavity shapes were reconstructed using a computer and the variation of myocardial elastic modulus was calculated, by the finite element method, through the passive phase of diastole when rising volume coincided with rising pressure. Geometric data were obtained from biplane cineangiography, with micromanometer pressure measurements, for ten patients with left ventricular disease. Dimensional analysis was applied to the initial and derived data from which the influences of myocardial compliance, wall thickness-to-long dimension ratio, and aspect ratio (long-to-short axes) were determined. The ratio between the volume elasticity and the myocardial modulus of elasticity, the normalized stiffness ratio (NSR), is proposed as a useful index of left ventricular mechanical behaviour in diastole. The volume elasticity of the chamber is dependent not only upon the myocardium elastic modulus and the wall thickness ratio, but also on the shape of the chamber. Changes in the thickness/radius ratio of the ventricle have less effect upon its distention than those in the long dimension/radius ratio. The left ventricle becomes more spherical in shape through diastole and hence becomes stiffer by this geometric mechanism. PMID:1569735
Modified face seal for positive film stiffness
NASA Technical Reports Server (NTRS)
Etsion, I.; Lipshitz, A. (inventors)
1981-01-01
The film stiffness of a face seal is improved without increasing the sealing and dam area by using an apparatus which includes a primary seal ring in the form of a nose piece. A spring forces a sealing surface on the seal ring into sealing contact with a seat to form a face seal. A circumferential clearance seal is formed in series with this face seal by a lip on the piece. The width of the surface of the lip is substantially the same as the width of the sealing surface on the face seal and the clearance between the surface on the lip and the shaft is substantially the same as the spacing between the face sealing surfaces on the face seal when the shaft is rotating. The circumferential clearance seal restricts the flow of fluid from a main cavity to an intermediate cavity with a resulting pressure drop. The hydrostatic opening face is strongly dependent on the face seal clearance, and the desired axial stiffness is achieved.
Towards ultra-stiff materials: Surface effects on nanoporous materials
Lu, Dingjie; Xie, Yi Min; Huang, Xiaodong; Zhou, Shiwei, E-mail: shiwei.zhou@rmit.edu.au [Centre for Innovative Structures and Materials, School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne 3001 (Australia); Li, Qing [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, New South Wales 2006 (Australia)
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.
Stiffness Analysis Of Multi-Chain Parallel Robotic Systems
Pashkevich, Anatoly; Wenger, Philippe
2008-01-01
The paper presents a new stiffness modelling method for multi-chain parallel robotic manipulators with flexible links and compliant actuating joints. In contrast to other works, the method involves a FEA-based link stiffness evaluation and employs a new solution strategy of the kinetostatic equations, which allows computing the stiffness matrix for singular postures and to take into account influence of the internal forces. The advantages of the developed technique are confirmed by application examples, which deal with stiffness analysis of the Orthoglide manipulator.
Stiffness Analysis Of Multi-Chain Parallel Robotic Systems
Pashkevich, Anatoly; Chablat, Damien; Wenger, Philippe
2009-01-01
The paper presents a new stiffness modelling method for multi-chain parallel robotic manipulators with flexible links and compliant actuating joints. In contrast to other works, the method involves a FEA-based link stiffness evaluation and employs a new solution strategy of the kinetostatic equations, which allows computing the stiffness matrix for singular postures and to take into account influence of the external forces. The advantages of the developed technique are confirmed by application examples, which deal with stiffness analysis of a parallel manipulator of the Orthoglide family
Two non-comoving stiff fluids in radial motion and spherical symmetry
Valentin Kostov
2008-11-04
The problem of two stiff fluids (energy density = pressure) moving radially in spherical symmetry is treated. The metric ansatz is chosen spherically symmetric, conformally static with a multiplicative separation of variables. The first fluid is described mathematically via a massless scalar field. The coordinate system is chosen comoving with the second fluid which the separation of variables requires to be stiff too. The fluids are interacting only gravitationally and their energy momentum tensors are separately conserved. The Einstein equations are reduced to a single nonlinear ODE of second order which is shown to lead to an Abel ODE. A few particular exact solutions were found using a polynomial ansatz. The two non-comoving gravitational sources in the solutions can be interpreted either as scalar fields or stiff fluids. A complete analysis is performed on the range of parameters for which the stiff fluid interpretation is physically acceptable. General formulas are derived for the conformal vectors of the solutions. By making the second fluid vanish, a few single scalar field solutions are generated some of which appear to be new. All solutions considered in this paper have a time-like singularity at the origin (except the trivial FRW one) and are not asymptotically flat (except the static one with k=0).
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.
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.
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
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
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
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.
Pratt, Jon R.; Shaw, Gordon A. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Kumanchik, Lee [Department of Mechanical Engineering, University of Florida, Gainesville, Florida 32611 (United States); Burnham, Nancy A. [Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609-2280 (United States)
2010-02-15
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.
Study of ultrasound stiffness imaging methods using tissue mimicking phantoms.
Manickam, Kavitha; Machireddy, Ramasubba Reddy; Seshadri, Suresh
2014-02-01
A pilot study was carried out to investigate the performance of ultrasound stiffness imaging methods namely Ultrasound Elastography Imaging (UEI) and Acoustic Radiation Force Impulse (ARFI) Imaging. Specifically their potential for characterizing different classes of solid mass lesions was analyzed using agar based tissue mimicking phantoms. Composite tissue mimicking phantom was prepared with embedded inclusions of varying stiffness from 50 kPa to 450 kPa to represent different stages of cancer. Acoustic properties such as sound speed, attenuation coefficient and acoustic impedance were characterized by pulse echo ultrasound test at 5 MHz frequency and they are ranged from (1564 ± 88 to 1671 ± 124 m/s), (0.6915 ± 0.123 to 0.8268 ± 0.755 db cm(-1)MHz(-1)) and (1.61 × 10(6) ± 0.127 to 1.76 × 10(6) ± 0.045 kg m(-2)s(-1)) respectively. The elastic property Young's Modulus of the prepared samples was measured by conducting quasi static uni axial compression test under a strain rate of 0.5mm/min upto 10 % strain, and the values are from 50 kPa to 450 kPa for a variation of agar concentration from 1.7% to 6.6% by weight. The composite phantoms were imaged by Siemens Acuson S2000 (Siemens, Erlangen, Germany) machine using linear array transducer 9L4 at 8 MHz frequency; strain and displacement images were collected by UEI and ARFI. Shear wave velocity 4.43 ± 0.35 m/s was also measured for high modulus contrast (18 dB) inclusion and X.XX m/s was found for all other inclusions. The images were pre processed and parameters such as Contrast Transfer Efficiency and lateral image profile were computed and reported. The results indicate that both ARFI and UEI represent the abnormalities better than conventional US B mode imaging whereas UEI enhances the underlying modulus contrast into improved strain contrast. The results are corroborated with literature and also with clinical patient images. PMID:24083832
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
Stiffness regulation by reflex action in the normal human hand.
Carter, R R; Crago, P E; Keith, M W
1990-07-01
1. The torque and electromyographic (EMG) responses to stretch of the first dorsal interosseous muscle (externally imposed joint rotation) were recorded in five normal human subjects. The total measured stiffness was decomposed into three individual stiffness components; passive, intrinsic, and reflex. 2. The passive component was measured with the subject relaxed. Compared with the total response at the height of short latency reflex action, the passive component comprised 6-32% of the total stiffness recorded at an initial torque level of 20 N-cm [15-39% maximum voluntary contraction (MVC)]. The passive response also reflected a significant acceleration component during rapid joint rotation due primarily to digit inertia. 3. The intrinsic stiffness component, attributed to the mechanical properties of the active muscle fibers, was estimated by recording the response to joint rotation with the muscle activated in a distributed manner using a single intramuscular electrode. The dynamic stiffness (measured at the end of a ramp displacement) and the static stiffness (measured 1 s after onset of the displacement) both scaled in a straight-line manner with the initial torque level. This relationship held whether the initial torque level was varied by changes in recruitment or temporal summation. 4. The reflex component was calculated by subtracting the passive and the estimated intrinsic component from the total response. The timing of the EMG signal recorded during measurement of the total response and the fact that the estimated intrinsic component matched the total active response over the first 65-100 ms after displacement onset supported the case that this was the true reflex component. The peak of the reflex activity occurred 155-360 ms after displacement onset and, at this peak, accounted for 18-44% of the total stiffness (at an initial torque level of 20 N-cm). 5. Over the low to intermediate torque range employed, we observed that both intrinsic muscle stiffness and total stiffness increased with initial torque. Because total stiffness increased more rapidly than intrinsic stiffness, the difference between them (equal to reflex stiffness) also increased with initial torque. Furthermore, when the total active response trials (passive stiffness removed) were shifted vertically so that the initial torque levels matched, it was seen that reflex action did not reduce the stiffness range to less than the stiffness range encountered for the intrinsic response alone.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:2388060
Effect of femoral stiffness on bone remodeling after uncemented arthroplasty.
Sychterz, C J; Topoleski, L D; Sacco, M; Engh, C A
2001-08-01
The current study examined the relationships among femoral stiffness, implant stiffness, and bone remodeling in 40 femurs retrieved at autopsy from 20 patients with unilateral uncemented hip replacements. The purpose of the study was to determine if the magnitude of periprosthetic bone loss after arthroplasty was correlated with, and could be predicted from, stem and femoral stiffness terms. For analysis, the contralateral normal femur was used as a control to represent the unremodeled condition of the in vivo implanted femur. Bone loss attributable to remodeling was quantified by video-densitometric analysis. Stiffness terms were calculated as the product of the elastic modulus and geometric properties digitized from cross-sectional slab radiographs. Femoral stiffness calculations accounted for variations in modulus attributable to patient differences in bone mineral density and geometric properties attributable to differences in the shape of individual femurs. Similarly, calculations of implant stiffness accounted for variations in implant shape. Results showed axial bone stiffness was the variable most strongly correlated with bone loss. Individual stem stiffness terms were not significantly correlated with bone loss. Multiple linear regression analysis, using stem-to-bone stiffness ratios as independent variables, accounted for 46% of the variance in bone loss data. In the regression analysis, the axial stem-to-bone stiffness ratio was the strongest correlate with bone loss. Although these results show the influence of mechanical stiffness factors on bone remodeling, other factors (hormonal status, drugs, disease, activity level) could represent the variance in bone loss data not accounted for in the study. PMID:11501814
NASA Technical Reports Server (NTRS)
Rouvas, C.; Childs, D. W.
1993-01-01
In identifying the rotordynamic coefficients of a high-Reynolds-number hydrostatic bearing, fluid-flow induced forces present a unique problem, in that they provide an unmeasureable and uncontrollable excitation to the bearing. An analysis method is developed that effectively eliminates the effects of fluid-flow induced excitation on the estimation of the bearing rotordynamic coefficients, by using power spectral densities. In addition to the theoretical development, the method is verified experimentally by single-frequency testing, and repeatability tests. Results obtained for a bearing are the twelve rotordynamic coefficients (stiffness, damping, and inertia coefficients) as functions of eccentricity ratio, speed, and supply pressure.
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.
Threshold bracing stiffness of two story frames
Khader, Ghassan Sudki
1982-01-01
. 6 and rewriting in matrix form gives P = K'd 48 tH 2 03 P (a) pz~6z pz~g Ps~&z P mz, 6z mz, 6z mz, 6z mq, 6z M- Pz Pz Pz (b) Fig. 17. ? Continuous Beam with Axial Force 49 f P1 61 B, Pz 62 P 3 63 B3 (4. 7) 1 1 1 1 K11 Kzz K13 K14 0... and simplifying gives 2P K h (1. 5) At the buckling load P equation 1. 5 becomes cr P K = 2? cr h (1. 6) Equation 1. 6 gives an easy to calculate upper bound value of the re- quired stiffness to have a braced frame. Equation 1, 6, however, is valid only...
Cartesian stiffness control of the JPL\\/Stanford\\/Salisbury hand
G. P. Starr
1988-01-01
To be useful as a dexterous end effector in assembly operations, a multifingered hand must be position-controlled to allow preshaping, and force-controlled to apply and regulate grasp forces. The author describes an implementation of stiffness control on the Salisbury hand, from tendon tension control to coordinated Cartesian object stiffness control. Substantial joint friction effects were observed which were predicted well
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 (0.048–0.64 N m?1) to tune the boundary stiffness of suspended collagen gels in between the commonly utilized free and fixed conditions (zero and infinite stiffness boundary stiffness). We demonstrate the principle of operation with finite element analyses and a wide range of experimental studies. In all cases, boundary stiffness has a strong influence on cell behavior, most notably eliciting higher basal tension and activated force (in response to KCl) and more pronounced remodeling of the collagen matrix at higher boundary stiffness levels. Measured equibiaxial forces for gels seeded with 3 million human foreskin fibroblasts range from 0.05 to 1 mN increasing monotonically with boundary stiffness. Estimated force per cell ranges from 17 to 100 nN utilizing representative volume element analysis. This device provides a valuable tool to independently study the effect of the mechanical environment of the cell in a 3D collagen matrix. PMID:20012205
Joint Stiffness Identification of Industrial Serial Robots Claire Dumasa
Paris-Sud XI, Université de
Joint Stiffness Identification of Industrial Serial Robots Claire Dumasa , St´ephane Caroa , Mehdi a new methodology for the joint stiffness identification of industrial serial robots and as consequence for the evaluation of both translational and rotational displacements of the robot's end-effector subject
a Study of Stiff Converging Problems in Magnetic Field Calculation
Mohammad Ali Golbazi
1985-01-01
This thesis is mainly devoted to the numerical solutions of stiff converging problems in magnetic fields. Stiff problems are the ones whose converging process in iterative methods is extremely slow. The solution of many micromagnetic problems lead to unbounded nonlinear partial differential equations. A standard technique to convert these problems to boundary value problems is to assume that the geometry
Kinetics of stiff-legged gait: induced acceleration analysis
Patrick O. Riley; D. Casey Kerrigan
1999-01-01
Treating spastic paretic stiff-legged gait, defined as reduced knee flexion in swing, holds a high priority in the rehabilitation of patients with upper motor neuron lesions. We propose a method to determine the relative contributions of hip, knee, and ankle inpairments to this disability. We analyzed the gait of ten patients with stiff-legged gait (SLG) due to a single stroke
Intelligent Compliance Control for Robot Manipulators Using Adaptive Stiffness Characteristics
Byoung-ho Kim; Nak Young Chong; Oh Sang-rok; Il Hong Suh; Young-jo Cho
1999-01-01
A compliance control strategy for robot manipulators is proposed by employing a self-adjusting stiffness function. To be specific, each entry of the diagonal stiffness matrix corresponding to task coordinate in Cartesian space is adaptively adjusted during contact along the corresponding axis based on the contact force with its environment. It can also be used for both unconstrained and constrained motions
Stiffness Matrix Synthesis Algorithms for Pre-loaded Planar Structures
Hyun Geun Yu; Rodney G. Roberts
2006-01-01
The force regulation and inevitable positional inaccuracy of traditional control system can be compensated by the compliance\\/stiffness mechanism. The compliance\\/stiffness of a robotic mechanism is usually modeled by a 6 by 6 symmetric positive definite matrix at an equilibrium point using screw theory. When an external wrench is exerted on the mechanism and the mechanism moves away from its equilibrium,
Note on the normal form of a spatial stiffness matrix
Rodney G. Roberts
2001-01-01
There has been some recent interest in the problem of designing compliance mechanisms with a given spatial stiffness matrix. A key result that has proven useful in the design of such mechanisms is Loncaric's normal form. When a spatial stiffness matrix is described in an appropriate coordinate frame, it will have a particularly simple structure. In this form the 3×3
A Systematic Analytical Method for PKM Stiffness Matrix Calculation
Dominique Deblaise; Xavier Hernot; Patrick Maurine
2006-01-01
The purpose of this work is to propose a new approach for the calculation of PKM stiffness matrix by using an analytical method based on matrix structural analysis. This method has as the main advantage to be systematic and it also can be applied to hyper-static PKM stiffness analysis. The implementation of the proposed method is fast and convenient and
A methodology for joint stiffness identification of serial robots
Claire Dumas; Stephane Caro; Mehdi Cherif; Sebastien Garnier; Benoit Furet
2010-01-01
This paper presents a new methodology for joint stiffness identification of serial robots. This methodology aims at evaluating all joint stiffness values responsible for both translational and rotational displacements of the robot end-effector subject to an external wrench (force and torque). The links of the robot are supposed to be quite stiffer than the joints and not known as it
Modeling and Control of Stiff Robots for Flexible Manufacturing
and conceptual flexibility of a robot for SMEs. Additionally, concepts that aid the SMEs to achieve the requiredModeling and Control of Stiff Robots for Flexible Manufacturing #12;#12;Modeling and Control of Stiff Robots for Flexible Manufacturing Isolde Dressler Department of Automatic Control Lund University
Column dampers with negative stiffness: high damping at small amplitude
Lakes, Roderic
! 1! Column dampers with negative stiffness: high damping at small amplitude adapted from Kalathur, H., Lakes, R. S., Column dampers with negative stiffness: high damping at small amplitude, Smart negative; the moduli become complex to allow viscoelastic behavior. As modulus is tuned, damping
Aerodynamic stiffness effects in rotational galloping at high wind speeds
B. W. van Oudheusden
1996-01-01
An investigation is made of aerodynamic stiffness effects on the dynamics of rotational galloping at high wind speeds. The system is analysed as a perturbation of the Hamiltonian system in which the aerodynamic stiffness is included. The analysis agrees with the experimentally observed behaviour. Both the frequency and mode shape of the oscillation are affected, while the amplitude of the
Measuring Interfacial Stiffness of Adhesively-Bonded Wood
Nairn, John A.
1 Measuring Interfacial Stiffness of Adhesively-Bonded Wood Edward A. Le FPInnovations - Engineered Interfacial Stiffness of Adhesively-Bonded Wood Abstract Future Abstract (100 to 150 words) 1. Introduction Adhesive bonds in wood composites have two roles. The first is to hold elements of the composite together
[Anesthetic management of a patient with stiff-person syndrome undergoing thymectomy].
Tadokoro, Takahiro; Yamashita, Soichiro; Ishigaki, Maiko; Takahashi, Shinji; Tanaka, Makoto
2012-02-01
Stiff-person syndrome is an uncommon disease characterized by muscular rigidity and painful spasms in the axial and limb muscles. We report a 58-year-old woman with stiff-person syndrome undergoing thymectomy under general anesthesia. Before surgery, her medications were 25 mg of diazepam, 2 mg of clonazepam, and 15 mg of gabapentin per day. After epidural catheterization for the postoperative analgesia, general anesthesia was induced and maintained with continuous remifentanil infusion and propofol with target controlled infusion. With train-of-four ratio (TOFR) monitoring by stimulating the ulnar nerve, her trachea was intubated after 0.6mg x kg(-1) of rocuronium intravenous administration. Since then, additional rocuronium was not given for 4 hours. After surgery, she was fully awake and TOFR recovered to 100%, but tidal volume was too low to remove the tracheal tube, and mechanical ventilation was continued in ICU. On the next day, the tracheal tube was removed, and she was discharged from ICU. Because anesthetics may delay the recovery of respiratory function in a patient with stiff-person syndrome, careful assessment of respiratory function is needed at the emergence from general anesthesia. PMID:22413445
Larivière, Christian; Ludvig, Daniel; Kearney, Robert; Mecheri, Hakim; Caron, Jean-Maxime; Preuss, Richard
2015-01-21
This study aimed at testing the reliability and construct validity of a trunk perturbation protocol (TPP) that estimates the intrinsic and reflexive contributions to low-back stiffness. The TPP consists of a series of pseudorandom position-controlled trunk perturbations in an apparatus measuring forces and displacements at the harness surrounding the thorax. Intrinsic and reflexive contributions to low-back stiffness were estimated using a system identification procedure, leading to 12 parameters. Study 1 methods (reliability): 30 subjects performed five 75-s trials, on each of two separate days (eight weeks apart). Reliability was assessed using the generalizability theory, which allowed computing indexes of dependability (?, analogous to intraclass correlation coefficient) and standard errors of measurement (SEM). Study 2 methods (validity): 20 healthy subjects performed three 75-s trials for each of five experimental conditions assumed to provide different lumbar stiffness; testing the construct validity of the TPP using four conditions with different lumbar belt designs and one control condition without. Study 1 results (reliability): Learning was seen between the first and following trials. Consequently, reliability analyses were performed without the first trial. Simulations showed that averaging the scores of three trials can lead to acceptable reliability results for some TPP parameters. Study 2 results (validity): All lumbar belt designs increased low-back intrinsic stiffness, while only some of them decreased reflex stiffness, which support the construct validity of the TPP. Overall, these findings support the use of the TPP to test the effect of rehabilitation or between-groups differences with regards to trunk stiffness. PMID:25529140
Relative contributions of age and atherosclerosis to vascular stiffness.
Santelices, Linda C; Rutman, Sarah J; Prantil-Baun, Rachelle; Vorp, David A; Ahearn, Joseph M
2008-05-01
To determine the relative contributions of aging and atherosclerosis to vascular stiffness, we studied aortic stiffness, plaque, and elastin in 8-, 16-, 25-, and 34-week-old male ApoE-KO and C57BL/6J control mice (N = 48). Stiffness increased gradually in both strains up to 25 weeks (p < 0.05), and dramatically between 25 and 34 weeks in ApoE-KO (p < 0.001). Aging ApoE-KO demonstrated increased plaque (p = 0.02), medial thickening (p < 0.001), and severe elastin fragmentation (p < 0.001). We conclude that the contribution of aging to vascular stiffness is relatively minor compared with the influence of atherosclerosis. However, the effect of atherosclerosis on stiffness is significant only with advanced stages of plaque formation. PMID:20443820
Characterization of the bending stiffness of large space structure joints
NASA Technical Reports Server (NTRS)
Wu, K. Chauncey
1989-01-01
A technique for estimating the bending stiffness of large space structure joints is developed and demonstrated for an erectable joint concept. Experimental load-deflection data from a three-point bending test was used as input to solve a closed-form expression for the joint bending stiffness which was derived from linear beam theory. Potential error sources in both the experimental and analytical procedures are identified and discussed. The bending stiffness of a mechanically preloaded erectable joint is studied at three applied moments and seven joint orientations. Using this technique, the joint bending stiffness was bounded between 6 and 17 percent of the bending stiffness of the graphite/epoxy strut member.
Diagnosing Aorta Stiffness by Temporal Analysis of Echocardiographic Images
NASA Astrophysics Data System (ADS)
Cheng, Yu-Hsi; Yen, Tsu-Chiang; Lee, Doyal
2005-03-01
In the diagnosis of cardiovascular diseases, information about the intracardiac system function and blood flow can be obtained by echocardiography due to its high spatial resolution capability. However, seldom message is known about the aorta stiffness. This work investigated a method to quantitatively analyze the aorta stiffness. The aorta was modeled as a periodic-force-driven damping oscillator, in which the aorta stiffness was the damping factor. From the analysis of echocardiographic images, the delay time of the maximal aorta distention relative to the R-peak of the electrocardiographic trace was measured to reveal the aorta stiffness. A study based on 10 samples suggested that a delay time greater than 0.17 sec could be a criterion to diagnose that the aorta is quite stiff. This method could also clearly discern some abnormal cardiac performance. A large-scale study with this method should be conducted in the future.
Stiffness coupling application to modal synthesis program, users guide
NASA Technical Reports Server (NTRS)
Kuhar, E. J.
1976-01-01
A FORTRAN IV computer program used to perform modal synthesis of structures by stiffness coupling, using the dynamic transformation method is described. The program was named SCAMP (Stiffness Coupling Approach Modal-Synthesis Program). The program begins with the entry of a substructure's physical mode shapes and eigenvalues or a substructure's mass and stiffness matrix. If the mass and stiffness matrices are entered, the eigen problem for the individual substructure is solved. Provisions are included for a maximum of 20 substructures which are coupled by stiffness matrix springs. Each substructure has a number degrees of freedom (DOF), except that for DOF greater than 100; vector sets having maximum row and column size of 100 were generated prior to entering SCAMP. The substructures are then coupled together via coupling springs, and the dynamic transformation is used to reduce the size of the eigen problem.
ORFEUS CFRP structure: A high stiffness-low thermal strain space telescope structure
NASA Astrophysics Data System (ADS)
Schaeffler, Thomas
1991-10-01
ORFEUS (Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer) is a 1 m diameter telescope to be integrated into the ASTRO-SPAS satellite on one of its missions. ORFEUS is to be launched in 1992 for a 7 day mission on the Space Shuttle. Design constraints to be respected during the development of the tube shaped structure with 4 m length and 1.1 m inner diameter were: lowest coefficient of thermal expansion, high stiffness, low outgassing rates and low mass. These constraints led to a filament wound tube stiffened on the outer side with autoclave cured CFRP (Carbon Fiber Reinforced Plastic) profiles. Material used is a high modulus carbon fiber in combination with epoxy resin. Flanges and other interfaces are mainly made of a low coefficient of thermal expansion nickel iron alloy Invar. An Invar foil covers the inner surface of the tube to restrict outgassing.
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
DESIGN, FABRICATION AND EVALUATION OF NEGATIVE STIFFNESS ELEMENTS USING SELECTIVE LASER SINTERING*
Seepersad, Carolyn Conner
negative stiffness behavior and thereby increase the damping and shift the resonant frequency sintering, negative stiffness, bistable structure, transmissibility, damping, energy absorption 1 and vibrational damping. Examples of negative stiffness mechanisms include mechanical systems with bistable
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.
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
Constraints Coefficients in hp-FEM Andreas Schroder
Schroeder, Andreas
Constraints Coefficients in hp-FEM Andreas SchrÂ¨oder Abstract Continuity requirements on irregular is given by the so-called constraints coefficients. Andreas SchrÂ¨oder Department of Mathematics, Humboldt.schroeder@mathematik.hu-berlin.de 1 #12;2 Andreas SchrÂ¨oder In a very general manner, constraints coefficients are defined as follows
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.
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.
Polyelectrolyte multilayer films of controlled stiffness modulate myoblast cells differentiation
Ren, Kefeng; Crouzier, Thomas; Roy, Christian; Picart, Catherine
2008-01-01
Beside chemical properties and topographical features, mechanical properties of gels have been recently demonstrated to play an important role in various cellular processes, including cell attachment, proliferation, and differentiation. In this work, we used multilayer films made of poly(L-lysine)/Hyaluronan (PLL/HA) of controlled stiffness to investigate the effects of mechanical properties of thin films on skeletal muscle cells (C2C12 cells) differentiation. Prior to differentiation, cells need to adhere and proliferate in growth medium. Stiff films (E0 > 320 kPa) promoted formation of focal adhesions and organization of the cytoskeleton as well as an enhanced proliferation, whereas soft films were not favorable for cell anchoring, spreading or proliferation. Then C2C12 cells were switched to a low serum containing medium to induce cell differentiation, which was also greatly dependent on film stiffness. Although myogenin and troponin T expressions were only moderately affected by film stiffness, the morphology of the myotubes exhibited striking stiffness-dependent differences. Soft films allowed differentiation only for few days and the myotubes were very short and thick. Cell clumping followed by aggregates detachment could be observed after ~2 to 4 days. On stiffer films, significantly more elongated and thinner myotubes were observed for up to ~ 2 weeks. Myotube striation was also observed but only for the stiffer films. These results demonstrate that film stiffness modulates deeply adhesion, proliferation and differentiation, each of these processes having its own stiffness requirement. PMID:18841249
Efficient computation of kinship and identity coefficients on large pedigrees.
Cheng, En; Elliott, Brendan; Ozsoyoglu, Z Meral
2009-06-01
With the rapidly expanding field of medical genetics and genetic counseling, genealogy information is becoming increasingly abundant. An important computation on pedigree data is the calculation of identity coefficients, which provide a complete description of the degree of relatedness of a pair of individuals. The areas of application of identity coefficients are numerous and diverse, from genetic counseling to disease tracking, and thus, the computation of identity coefficients merits special attention. However, the computation of identity coefficients is not done directly, but rather as the final step after computing a set of generalized kinship coefficients. In this paper, we first propose a novel Path-Counting Formula for calculating generalized kinship coefficients, which is motivated by Wright's path-counting method for computing inbreeding coefficient. We then present an efficient and scalable scheme for calculating generalized kinship coefficients on large pedigrees using NodeCodes, a special encoding scheme for expediting the evaluation of queries on pedigree graph structures. Furthermore, we propose an improved scheme using Family NodeCodes for the computation of generalized kinship coefficients, which is motivated by the significant improvement of using Family NodeCodes for inbreeding coefficient over the use of NodeCodes. We also perform experiments for evaluating the efficiency of our method, and compare it with the performance of the traditional recursive algorithm for three individuals. Experimental results demonstrate that the resulting scheme is more scalable and efficient than the traditional recursive methods for computing generalized kinship coefficients. PMID:19507284
SLE?: correlation functions in the coefficient problem
NASA Astrophysics Data System (ADS)
Loutsenko, Igor
2012-07-01
We apply the method of correlation functions to the coefficient problem in stochastic geometry. In particular, we give a proof for some universal patterns conjectured by M Zinsmeister for the second moments of the Taylor coefficients for special values of ? in the whole-plane Schramm-Loewner evolution (SLE?). We propose to use multi-point correlation functions for the study of higher moments in the coefficient problem. Generalizations related to the Levy-type processes are also considered. The exact integral means ?-spectrum of this version of the whole-plane SLE? is discussed.
Urban, M.W.; Fatemi, M.; Greenleaf, J.F.
2011-01-01
This paper reports shear stiffness and viscosity “virtual biopsy” measurements of three excised non-cancerous human prostates using shearwave dispersion ultrasound vibrometry (SDUV) in vitro. Improved methods for prostate guided-biopsy are required to effectively guide needle biopsy to the suspected site. In addition, tissue stiffness measurement helps identifying a suspected site to perform biopsy because stiffness has been shown to correlate with pathology. More importantly, early detection of prostate cancer may guide minimally-invasive therapy and eliminate insidious procedures. In this work, “virtual” biopsies were taken in multiple locations in three excised prostates. Then, SDUV shear elasticity and viscosity measurements have been performed at the selected “suspicious” locations within the prostates. SDUV measurements of prostate elasticity and viscosity are generally in agreement with preliminary values reported previously in the literature. It is however important to emphasize that the obtained viscoelastic parameters values are local, and not a mean value for the whole prostate. PMID:20595086
Enhancement of structural stiffness in MEMS structures
NASA Astrophysics Data System (ADS)
Ilias, Samir; Picard, Francis; Topart, Patrice; Larouche, Carl; Jerominek, Hubert
2006-01-01
Many optical applications require smooth micromirror reflective surfaces with large radius of curvature. Usually when using surface micromachining technology and as a result of residual stress and stress gradient in thin films, the control of residual curvature is a difficult task. In this work, two engineering approaches were developed to enhance structural stiffness of micromirrors. 1) By integrating stiffening structures and thermal annealing. The stiffening structures consist of U-shaped profiles integrated with the mirror (dimension 200×300 ?m2). 2) By combining selective electroplating and flip-chip based technologies. Nickel was used as electroplated material with optimal stress values around +/-10 MPa for layer thicknesses of about 10 ?m. With the former approach, typical curvature radii of about 1.5 cm and 0.6 cm along mirror width and length were obtained, respectively. With the latter approach, an important improvement in the micromirror planarity and flatness was achieved with curvature radius up to 23 cm and roughness lower than 5 nm rms for typical 1000×1000 ?m2 micromirrors.
Keeney, Michael; Onyiah, Sheila; Zhang, Zhe; Tong, Xinming; Han, Li-Hsin; Yang, Fan
2013-12-01
Non-viral gene delivery holds great promise for promoting tissue regeneration, and offers a potentially safer alternative than viral vectors. Great progress has been made to develop biodegradable polymeric vectors for non-viral gene delivery in 2D culture, which generally involves isolating and modifying cells in vitro, followed by subsequent transplantation in vivo. Scaffold-mediated gene delivery may eliminate the need for the multiple-step process in vitro, and allows sustained release of nucleic acids in situ. Hydrogels are widely used tissue engineering scaffolds given their tissue-like water content, injectability and tunable biochemical and biophysical properties. However, previous attempts on developing hydrogel-mediated non-viral gene delivery have generally resulted in low levels of transgene expression inside 3D hydrogels, and increasing hydrogel stiffness further decreased such transfection efficiency. Here we report the development of biodegradable polymeric vectors that led to efficient gene delivery inside poly(ethylene glycol) (PEG)-based hydrogels with tunable matrix stiffness. Photocrosslinkable gelatin was maintained constant in the hydrogel network to allow cell adhesion. We identified a lead biodegradable polymeric vector, E6, which resulted in increased polyplex stability, DNA protection and achieved sustained high levels of transgene expression inside 3D PEG-DMA hydrogels for at least 12 days. Furthermore, we demonstrated that E6-based polyplexes allowed efficient gene delivery inside hydrogels with tunable stiffness ranging from 2 to 175 kPa, with the peak transfection efficiency observed in hydrogels with intermediate stiffness (28 kPa). The reported hydrogel-mediated gene delivery platform using biodegradable polyplexes may serve as a local depot for sustained transgene expression in situ to enhance tissue engineering across broad tissue types. PMID:24011715
Leg stiffness and joint stiffness while running to and jumping over an obstacle.
Mauroy, G; Schepens, B; Willems, P A
2014-01-22
During running, muscles of the lower limb act like a linear spring bouncing on the ground. When approaching an obstacle, the overall stiffness of this leg-spring system (k(leg)) is modified during the two steps preceding the jump to enhance the movement of the center of mass of the body while leaping the obstacle. The aim of the present study is to understand how k(leg) is modified during the running steps preceding the jump. Since k(leg) depends on the joint torsional stiffness and on the leg geometry, we analyzed the changes in these two parameters in eight subjects approaching and leaping a 0.65 m-high barrier at 15 km h(-1). Ground reaction force (F) was measured during 5-6 steps preceding the obstacle using force platform and the lower limb movements were recorded by camera. From these data, the net muscular moment (M(j)), the angular displacement (?(j)) and the lever arm of F were evaluated at the hip, knee and ankle. At the level of the hip, the M(j)-?(j) relation shows that muscles are not acting like torsional springs. At the level of the knee and ankle, the M(j)-?(j) relation shows that muscles are acting like torsional springs: as compared to steady-state running, the torsional stiffness k(j) decreases from ~1/3 two contacts before the obstacle, and increases from ~2/3 during the last contact. These modifications in k(j) reflect in changes in the magnitude of F but also to changes in the leg geometry, i.e. in the lever arms of F. PMID:24275441
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
Nolan, Steven Anthony
1987-01-01
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... pattern seals had less net damping than the hole- pattern seal but more than the smooth seal. The stiffness was comparable to the hole' pattern seal. Both the sawtooth and hole-pattern seals leaked less than the smooth seal, while the sawtooth...
Wing/store flutter with nonlinear pylon stiffness
NASA Technical Reports Server (NTRS)
Desmarais, R. N.; Reed, W. H., III
1980-01-01
Recent wind tunnel tests and analytical studies show that a store mounted on a pylon with soft pitch stiffness provides substantial increase in flutter speed of fighter aircraft and reduces dependency of flutter on mass and inertia of the store. This concept, termed the decoupler pylon, utilizes a low frequency control system to maintain pitch alignment of the store during maneuvers and changing flight conditions. Under rapidly changing transient loads, however, the alignment control system may allow the store to momentarily bottom against a relatively stiff backup structure in which case the pylon stiffness acts as a hardening nonlinear spring. Such structural nonlinearities are known to affect not only the flutter speed but also the basic behavior of the instability. The influence of pylon stiffness nonlinearities or the flutter characteristics of wing mounted external stores is examined.
Arterial Stiffness and Renal Replacement Therapy: A Controversial Topic
Fischer, Edmundo Cabrera; Zócalo, Yanina; Galli, Cintia; Bia, Daniel
2015-01-01
The increase of arterial stiffness has been to have a significant impact on predicting mortality in end-stage renal disease patients. Pulse wave velocity (PWV) is a noninvasive, reliable parameter of regional arterial stiffness that integrates the vascular geometry and arterial wall intrinsic elasticity and is capable of predicting cardiovascular mortality in this patient population. Nevertheless, reports on PWV in dialyzed patients are contradictory and sometimes inconsistent: some reports claim the arterial wall stiffness increases (i.e., PWV increase), others claim that it is reduced, and some even state that it augments in the aorta while it simultaneously decreases in the brachial artery pathway. The purpose of this study was to analyze the literature in which longitudinal or transversal studies were performed in hemodialysis and/or peritoneal dialysis patients, in order to characterize arterial stiffness and the responsiveness to renal replacement therapy.
Dynamic study of tunable stiffness scanning microscope probe
Vega González, Myraida Angélica
2005-01-01
This study examines the dynamic characteristics of the in-plane tunable stiffness scanning microscope probe for an atomic force microscope (AFM). The analysis was carried out using finite element analysis (FEA) methods for ...
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)
Nanoindenter Stiffness Measurements on a MEMS Sound Sensor
NASA Astrophysics Data System (ADS)
Downey, R.; Brewer, L.; Karunasiri, G.
2012-02-01
We demonstrate a novel technique to extract the various components of the stiffness (or compliance) measured along the surface of a MEMS directional sound sensor. Because the sensor comprises a cantilever beam mounted on torsion springs, the overall stiffness consists of various compliance components added in series. Stiffness measurements made using a nanoindenter are found to agree with an analytical model and a finite element model (FEM) of the sensor. Moreover, by exploiting the differing power-law characteristics of the individual compliance components, we demonstrate extraction of the separate components from a logarithmic plot of the overall stiffness. Finally, we measure the ultimate (failure) strength of the sensor, from which we obtain the maximum acoustic intensity the sensor can tolerate.
Nondestrutive damage detection by simultaneous identification of stiffness and damping
Hyung, Sang Su
2009-05-15
The objective of this study is to develop a nondestructive damage evaluation methodology that can identify simultaneously both stiffness and damping changes in a structure. Two approaches are used to meet the stated objectives. First, a method...
Residual-based Stiffness Estimation in Robots with Flexible Transmissions
De Luca, Alessandro
joints with flexible transmissions. Based on the definition of dynamic residual signals, we derive/stiffness decoupling control law proposed in [4] for antagonistic VSA-based manipulators involves the transmission
Composite Materials with Viscoelastic Stiffness Greater Than Diamond
Lakes, Roderic
systems. For example, both negative stiffness and the resulting giant damping were observed (2 stabilizes the negative bulk modulus (inverse compressibility) of the inclusions. This negative modulus that exhibit negative refraction by inertial resonant effects. Conventional composites with positive
Quantification of Magnetically Induced Changes in ECM Local Apparent Stiffness
Herath, Sahan C.B.; Yue, Du; Hui, Shi; Kim, Min-Cheol; Wang, Dong-an; Wang, Qingguo; Van Vliet, Krystyn J.; Asada, Harry; Chen, Peter C.Y.
2014-01-01
The stiffness of the extracellular matrix (ECM) is known to influence cell behavior. The ability to manipulate the stiffness of ECM has important implications in understanding how cells interact mechanically with their microenvironment. This article describes an approach to manipulating the stiffness ECM, whereby magnetic beads are embedded in the ECM through bioconjugation between the streptavidin-coated beads and the collagen fibers and then manipulated by an external magnetic field. It also reports both analytical results (obtained by formal modeling and numerical simulation) and statistically meaningful experimental results (obtained by atomic force microscopy) that demonstrate the effectiveness of this approach. These results clearly suggest the possibility of creating desired stiffness gradients in ECM in vitro to influence cell behavior. PMID:24411265
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
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.
Geometrical Interpretation of the CCT Stiffness Mapping for Serial Manipulators
Chintien Huang; Imin Kao
2001-01-01
Recent research results suggested a conservative transformation to correct the well-known congruence transformation between\\u000a Cartesian and joint stiffness matrices of a serial manipulator. This paper utilizes screw geometry to interpret the conservative\\u000a congruence transformation (CCT). The analysis using screw theory provides better geometric insights into the CCT. The effective\\u000a geometrical stiffness matrix, due to the change of manipulator geometry under
Matrix cracking and bending stiffness reduction in composite laminates
Frailey, James Alan
1988-01-01
MATRIX CRACKING AND BENDING STIFFNESS REDUCTION IN COAIPOSITE LAMINATES A Thesis by JAMES ALAN FRAILEY Submitted to the Office of Graduate Studies of Texas AgcM University in partial fulfillment of the requirements for the degree of MASTER... OF SCIENCE December 1988 Major Subject: Aerospace Engineering MATRIX CRACKING AND BENDING STIFFNESS REDUCTION IN COMPOSITE LAMINATES A Thesis by JAMES ALAN FRAILEY Approved as to style and content by: A. L. High mith (Chair of Committee) W. E...
Cornering stiffness estimation based on vehicle lateral dynamics
C. Sierra; E. Tseng; A. Jain; H. Peng
2006-01-01
In this article, the cornering stiffness estimation problem based on the vehicle bicycle (one-track) model is studied. Both time-domain and frequency-domain-based methods are analyzed, aiming to estimate the effective cornering stiffness, defined as the ratio between the lateral force and the slip angle at the two axles. Several methods based on the bicycle model were developed, each having specific pros\\/cons
Boundary Stiffness Regulates Fibroblast Behavior in Collagen Gels
Jeffrey John; Angela Throm Quinlan; Chiara Silvestri; Kristen Billiar
2010-01-01
Recent studies have illustrated the profound dependence of cellular behavior on the stiffness of 2D culture substrates. The\\u000a goal of this study was to develop a method to alter the stiffness cells experience in a standard 3D collagen gel model without\\u000a affecting the physiochemical properties of the extracellular matrix. A device was developed utilizing compliant anchors (0.048–0.64 N m?1) to tune the
Generalized thermoelectric Thomson relations
L. I. Anatychuk; O. J. Luste
2003-01-01
Thermoelectric Thomson relations interrelating the Seebeck, Peltier and Thomson coefficients were generalized for anisotropic thermoelectric media in magnetic field with regard for possible Umkehr effect. From the restrictions imposed by space and time symmetry on the properties of anisotropic media in magnetic field it was shown that the first Thomson relation relating the generalized Peltier coefficient ?* to the generalized
Asymptotic coefficients for one-interacting-level Voigt profiles
NASA Astrophysics Data System (ADS)
Cope, D.; Lovett, R. J.
1988-02-01
The asymptotic behavior of general Voigt profiles with general width and shift functions has been determined by Cope and Lovett (1987). The resulting asymptotic coefficients are functions of the perturber/radiator mass ratio; also, the coefficients for the one-interacting-level (OIL) profiles proposed by Ward et al. (1974) were studied. In this paper, the behavior of the OIL asymptotic coefficients for large mass ratio values is determined, thereby providing a complete picture of OIL asymptotics for all mass ratios.
Substrate stiffness together with soluble factors affects chondrocyte mechanoresponses.
Chen, Cheng; Xie, Jing; Deng, Linhong; Yang, Liu
2014-09-24
Tissue cells sense and respond to differences in substrate stiffness. In chondrocytes, it has been shown that substrate stiffness regulates cell spreading, proliferation, chondrogenic gene expression, and TGF-? signaling. But how the substrate stiffness together with soluble factors influences the mechanical properties of chondrocyte is still unclear. In this study, we cultured goat articular chondrocytes on polyacrylamide gels of 1, 11, and 90 kPa (Young's modulus), and measured cellular stiffness, traction force, and response to stretch in the presence of TGF-?1 or IL-1?. We found that TGF-?1 increased cellular stiffness and traction force and enhanced the response to stretch, while IL-1? increased cellular stiffness, but lowered traction force and weakened the response to stretch. Importantly, the effects of TGF-?1 on chondrocyte mechanics were potent in cells cultured on 90 kPa substrates, while the effects of IL-1? were potent on 1 kPa substrates. We also demonstrated that such changes of chondrocyte mechanoresponse were due to not only the changes of actin cytoskeleton and focal adhesion, but also the alteration of chondrocyte extracellular matrix synthesis. Taken together, these results provide insights into how chondrocytes integrate physical and biochemical cues to regulate their biomechanical behavior, and thus have implications for the design of optimized mechanical and biochemical microenvironments for engineered cartilage. PMID:25162787
Coefficients of univalent functions
Peter L. Duren
1977-01-01
analytic and univalent in the unit disk \\\\z\\\\ < 1. This is the class of all univalent functions normalized by the conditions \\/(O) = 0 and \\/'(O) = 1. We shall concentrate on coefficient problems for the class S and for related classes, with emphasis on recent results and open problems. Most of the methods we shall describe have wide
Enhanced stiffness modeling of manipulators with passive joints Anatol Pashkevicha,b,*
Paris-Sud XI, Université de
stiffness matrix which allows rank-deficiency. Within the developed technique, the manipulator elements robots, which interact directly with humans, a rather low stiffness is required to eliminate collisions the mechanical stiffness of the manipulator (passive compliance) and the stiffness of the robotic system, which
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.
Arterial stiffness is increased in Hodgkin lymphoma survivors treated with radiotherapy.
van Leeuwen-Segarceanu, Elena M; Dorresteijn, Lucille D A; Vogels, Oscar J M; Biesma, Douwe H; Bos, Willem-Jan W
2013-08-01
Radiotherapy has been associated with an increased risk for cardiovascular disease (CVD) in Hodgkin lymphoma survivors (HLS). Identifying subjects most likely to develop these complications is challenging. Arterial stiffness has been frequently used as an early marker of CVD, but has never previously been investigated in patients treated with radiotherapy. The carotid-femoral pulse wave velocity (PWV) and the distensibility coefficient (DC) of the common carotid artery were used as markers of arterial stiffness. Eighty-two HLS and 40 age- and gender-matched control subjects were studied. The aorta and the carotid arteries were situated within the radiation field in 50 and 39 patients. Mean PWV was not significantly different in HLS treated with radiotherapy on the mediastinum when compared to HLS treated without mediastinal radiotherapy and to controls. If HLS were 40 years or older at radiotherapy their PWV was significantly higher (8.54 m/s) than patients irradiated at a younger age (7.14 m/s, p = 0.004) and controls (6.91 m/s, p < 0.001), after adjusting for current age and other CVD risk factors. Mean DC was lower, indicative of stiffer arteries, in HLS treated with radiotherapy on the common carotid artery (2.79) than in HLS without radiotherapy (3.35, p = 0.029) and versus controls (3.60, p = 0.001). DC was lowest in HLS treated at 35 years of age or later (2.05), compared to HLS irradiated at a younger age (2.98, p = 0.046). In HLS, radiotherapy is associated with increased arterial stiffness. The effect of radiotherapy seems most evident when radiotherapy is administered at ages above 35-40 years. PMID:23151008
Ogi, Hirotsugu; Hayama, Noritaka; Niho, Hiroki; Hirao, Masahiko; Morishita, Tomohiro
2007-08-01
The distribution of the local stiffness of a polycrystalline copper exposed to a creep test was studied by resonance ultrasound microscopy. The local effective modulus was evaluated from the resonance frequency of the isolated langasite oscillator touching the specimen. Defects appeared predominantly on grain boundaries, and they were clearly visualized by the stiffness microscopy through the significant decrease of the effective stiffness. The stiffness within the grains becomes lower regardless of invisible defects. The stiffness distribution was quantitatively analyzed by the contact model between two anisotropic bodies and by the micromechanics modeling. The microscopic stiffness shows much higher sensitivity to the defects than the macroscopic stiffness. PMID:17703654
Clinical relevance of right ventricular diastolic stiffness in pulmonary hypertension.
Trip, Pia; Rain, Silvia; Handoko, M Louis; van der Bruggen, Cathelijne; Bogaard, Harm J; Marcus, J Tim; Boonstra, Anco; Westerhof, Nico; Vonk-Noordegraaf, Anton; de Man, Frances S
2015-06-01
Right ventricular (RV) diastolic stiffness is increased in pulmonary arterial hypertension (PAH) patients. We investigated whether RV diastolic stiffness is associated with clinical progression and assessed the contribution of RV wall thickness to RV systolic and diastolic stiffness. Using single-beat pressure-volume analyses, we determined RV end-systolic elastance (Ees), arterial elastance (Ea), RV--arterial coupling (Ees/Ea), and RV end-diastolic elastance (stiffness, Eed) in controls (n=15), baseline PAH patients (n=63) and treated PAH patients (survival >5?years n=22 and survival <5?years n=23). We observed an association between Eed and clinical progression, with baseline Eed >0.53?mmHg·mL(-1) associated with worse prognosis (age-corrected hazard ratio 0.27, p=0.02). In treated patients, Eed was higher in patients with survival <5?years than in patients with survival >5?years (0.91±0.50 versus 0.53±0.33?mmHg·mL(-1), p<0.01). Wall-thickness-corrected Eed values in PAH patients with survival >5?years were not different from control values (0.76±0.47 versus 0.60±0.41?mmHg·mL(-1), respectively, not significant), whereas in patients with survival <5?years, values were significantly higher (1.52±0.91?mmHg·mL(-1), p<0.05 versus controls). RV diastolic stiffness is related to clinical progression in both baseline and treated PAH patients. RV diastolic stiffness is explained by the increased wall thickness in patients with >5?years survival, but not in those surviving <5?years. This suggests that intrinsic myocardial changes play a distinctive role in explaining RV diastolic stiffness at different stages of PAH. PMID:25882798
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 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400?kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture. PMID:25050406
Modeling of compressive stiffness of a multilayered graphite-reinforced magnesium-matrix composite
Bhattacharya, A.K.; Hong, S.I. (Los Alamos National Lab., NM (United States))
1993-06-01
Short graphite fiber-reinforced magnesium-matrix composites are of considerable interest due to their superior specific strength, stiffness and low coefficient of thermal expansion. The problem of non-wetting of fibers with molten metal in these composites seems to have been considerably improved and such types of composites are now being commercially produced. However, an understanding of the mechanical properties of these composites is very limited and less amenable to rigorous analysis because of the discontinuous fiber arrangements. Also, a part of the difficulty is due to a large number of geometrical and material variables arising in the analysis. The situation is further complicated when the composites are made of layered structure, each layer having different fiber orientations. Moreover, inherent porosity and its distribution in the layered composites cause further complicacy for it to be amenable for the mathematical analysis. In this note the authors discuss a finite element approach to the analysis of compressive stiffness behavior in such a composite and compare model predictions with experimental data on the modulus of such composites.
The Multidimensional Random Coefficients Multinomial Logit Model.
ERIC Educational Resources Information Center
Adams, Raymond J.; Wilson, Mark; Wang, Wen-chung
1997-01-01
Presents a multidimensional Rasch-type item response model, the multidimensional random coefficients multinomial logit model, which is developed in a form that permits generalization to the multidimensional case of a wide class of Rasch models. Derives marginal maximum likelihood estimators for the model. (SLD)
When Should Epidemiologic Regressions Use Random Coefficients?
Sander Greenland
2000-01-01
SUMMARY. Regression models with random coefficients arise naturally in both frequentist and Bayesian approaches to estimation problems. They are becoming widely available in standard computer packages under the headings of generalized linear mixed models, hierarchical models, and multilevel models. I here argue that such models offer a more scientifically defensible framework for epidemiologic analysis than the fixed-effects models now prevalent
Arterial Stiffness: A Novel Risk Factor for Kidney Injury Progression?
Georgianos, Panagiotis I; Sarafidis, Pantelis A; Liakopoulos, Vassilios
2015-08-01
Arterial stiffness is typical feature of vascular remodeling in chronic kidney disease (CKD). Increased arterial stiffness raises flow and pressure pulsatility and is considered the principle pathogenic mechanism of isolated systolic hypertension, left ventricular hypertrophy, and congestive heart failure. Apart from the impact of arterial stiffness on left ventricular afterload, downstream transmission of pressure pulsatility to the level of microcirculation is suggested to promote injury of other susceptible organs. This may be of particular importance for kidney injury progression, since passive renal perfusion along with low resistance and input impedance in renal microvessels make kidneys particularly vulnerable to the damaging effect of systemic pulsatile pressure. Recent studies have provided evidence that arterial stiffness culminates in elevated pulsatility and resistance in renal microvasculature, promoting structural damage of small intra-renal arterioles. Further, prospective observational studies have shown that reduced aortic compliance is closely associated with the annual rate of renal function decline and represents independent predictor of kidney injury progression to end-stage renal disease among patients with CKD. This article provides insights into the cross-talk between macrocirculation and renal microcirculation and summarizes the currently available clinical evidence linking increased arterial stiffness with kidney disease progression. PMID:25687879
Exchange Stiffness in Thin-Film Cobalt Alloys
NASA Astrophysics Data System (ADS)
Eyrich, Charles
The exchange stiffness, Aex, is one of the key parameters controlling magnetization reversal in magnetic materials but is very difficult to measure, especially in thin films. We developed a new technique for measuring the exchange stiffness of a magnetic material based on the formation of a spin spiral within two antiferromagnetically coupled ferromagnetic films [1]. Using this method, I was able to measure the exchange stiffness of thin film Co alloyed with Cr, Fe, Ni, Pd, Pt and Ru. The results of this work showed that the rate at which a substituent element reduces the exchange stiffness is not directly related to its effect on the magnetization of the alloy. These measured trends have been understood by combining measurements of element specific magnetic moments obtained using X-ray magnetic circular dichroism (XMCD) and material specific modeling based on density functional theory (DFT) within the local density approximation (LDA). The experimental results also hint at significant reduction of the exchange stiffness at the interface that can account for the difference between our results and those obtained on bulk materials.
Increased cardiovascular stiffness and impaired age-related functional status.
Andersen, Mousumi M; Kritchevsky, Stephen B; Morgan, Timothy M; Hire, Don G; Vasu, Sujethra; Brinkley, Tina E; Kitzman, Dalane W; Hamilton, Craig A; Soots, Sandra; Hundley, William G
2015-05-01
Our objective was to determine if increased cardiovascular (CV) stiffness is associated with disability in middle-aged and older adults at risk for congestive heart failure. CV stiffness (brachial pulse pressure/left ventricular stroke volume indexed to body surface area) and total disability (the summed assessment of activities of daily living, mobility, and instrumental activities of daily living) were measured in 445 individuals. A subset of 109 randomly selected individuals also underwent physical function testing. Total disability was associated with CV stiffness (p = .01), driven by an association with mobility (p = .005), but not activities of daily living (p = .13) or instrumental activities of daily living (p = .61). After accounting for age, these correlations remained significant for men (p = .04), but not for women. CV stiffness was also associated with increased 400-m walk time (p = .02). In middle-aged and elderly men at risk for congestive heart failure, CV stiffness is associated with decreased mobility and physical function, and increased overall disability. PMID:24963155
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
Variable stiffness material and structural concepts for morphing applications
NASA Astrophysics Data System (ADS)
Kuder, Izabela K.; Arrieta, Andres F.; Raither, Wolfram E.; Ermanni, Paolo
2013-11-01
Morphing, understood as the ability to undergo pronounced shape adaptations to optimally respond to a diversity of operational conditions, has been singled out as a future direction in the pursuit of maximised efficiency of lightweight structures. Whereas a certain degree of adaptivity can be accomplished conventionally by means of mechanical systems, compliance allowing for substantial reversible deformability exhibits far more potential as a morphing strategy. A promising solution to the inherent contradiction between high stiffness and reversible deformation capacity posed by morphing is offered by introducing variable stiffness components. This notion indicates the provision of a controllable range of deformation resistance levels in place of fixed properties, as required by real-time shape adaptation dictated by maximum efficiency under changing external conditions. With special emphasis on the morphing context, the current review aims to identify the main tendencies, undertaking a systematic classification of existing approaches involving stiffness variability. Four broad categories in which variable stiffness has been applied to morphing are therefore distinguished and detailed: material engineering, active mechanical design, semi-active techniques and elastic structural behaviour. Adopting a wide perspective, the study highlights key capabilities, limitations and challenges. The need for attention directed to the variable stiffness strategy is recognised and the significance of intensive research activities in a highly integrated and multidisciplinary environment emphasised if higher maturity stages of the concepts are to be reached. Finally, the potential of emerging directions of semi-active design involving electro-bonded laminates and multi-stable structures is brought into focus.
Chronic permanent hypoxemia predisposes to mild elevation of liver stiffness
Tahiri, Mohamed; Drighil, Abdenasser; Jalal, Yasmine; Ghellab, Dounia; Hliwa, Wafaa; Fouad, Haddad; Badre, Wafaa; Bellabah, Ahmad; Habbal, Rachida; Alaoui, Rhimou
2014-01-01
AIM: To evaluate the impact of long term permanent hypoxemia noticed in patients with non operated congenital cyanogenic cyanotic cardiopathy on liver stiffness. METHODS: We included ten adult patients with non operated inoperate cyanotic cardiopathy and ten matched patients for age and gender admitted to the gastroenterology department for proctologic diseases; Clinical and laboratory data were collected [age, gender, body mass index, oxygen saturation, glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), glycemia and cholesterol]. Measurement of hepatic stiffness by transient elastography was carried out in all patients using the Fibroscan device. All patients underwent an echocardiography to eliminate congestive heart failure. RESULTS: Among the patients with cyanotic cardiopathy, median liver stiffness 5.9 ± 1.3 kPa was greater than control group (4.7 ± 0.4 kPa) (P = 0.008). Median levels of GOT, GPT, gamma-glutamyltransferase, glycemia and cholesterol were comparable in cardiopathy and control group. In regression analysis including age, gender, body mass index, oxygen saturation, GOT, GPT, glycemia, cholesterol showed that only oxygen saturation was related to liver stiffness (r = -0.63 P = 0.002). CONCLUSION: Chronic permanent hypoxemia can induce mild increase of liver stiffness, but further studies are needed to explore the histological aspects of liver injury induced by chronic permanent hypoxemia. PMID:25132776
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
Probe stiffness regulates receptor-ligand bond lifetime under force
NASA Astrophysics Data System (ADS)
Zhang, Yan; Lü, ShouQin; Long, Mian
2011-05-01
Receptor-ligand bond dissociation under applied force is crucial to elucidate its biological functionality when the molecular bond is usually connected to a mechanical probe. While the impact of probe stiffness, k, on bond rupture force has recently attracted more and more attention, the mechanism of how it affects the bond lifetime, however, remains unclear. Here we quantified the dissociation lifetime of selectin-ligand bond using an optical trap assay with low stiffness ranging from 3.5×10-3 to 4.7×10-2 pN/nm. Our results indicated that bond lifetime yielded distinct distributions with different probe stiffness, implying the stochastic feature of bond dissociation. It was also found that the mean lifetime varied with probe stiffness and that the catch bond nature was visualized at k?3.0×10-2 pN/nm. This work furthered the understanding of the forced dissociation of selectin-ligand bond at varied probe stiffness, which is physiologically relevant to the tethered rolling of leukocytes under blood flow.
Stiffness characterisation of microcantilevers based on conducting polymers
NASA Astrophysics Data System (ADS)
Alici, Gursel; Higgins, Michael J.
2008-12-01
The object of this paper is to characterise the stiffness of microfabricated cantilevers consisting of two electroactive polymer (polypyrrole (PPy)) layers, and two gold layers with a negligible thickness and a layer of porous polyvinylidene fluoride (PVDF), which serves as a backing layer and electrolyte storage tank. This composite cantilever structure is used as polymer actuators or famously known as artificial muscles when tailored appropriately. The polymer microactuators considered in this study, which were fabricated using a laser ablation technique, could operate both in aqueous and non-aqueous media. The stiffness characterization of the microactuators is critical to assess their suitability to numerous applications including the micromanipulation of living cells, bio-analytical nanosystems, datastorage, labon- chip, microvalve, microswitch, microshutter, cantilever light modulators, micro-optical instrumentation, artificial muscles for micro and macro robotic sytems and similar. The stiffness measurement method followed in this study is a static deflection measurement method, using an atomic force microscope (AFM). The stiffness constants of the microactuators while they were in passive (no electrochemical activation) and active (electrochemically activated) states were measured separately, and their statistical comparison was provided. The possible error sources for the stiffness measurement method are elaborated.
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
Time-varying torsional stiffness identification on a vertical beam using Chebyshev polynomials
NASA Astrophysics Data System (ADS)
Martel, François; Rancourt, Denis; Chochol, Catherine; St-Amant, Yves; Chesne, Simon; Rémond, 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 6.62×10-2% 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.
Dynamic structure factor of a stiff polymer in a glassy solution
J. Glaser; O. Hallatschek; K. Kroy
2008-05-29
We provide a comprehensive overview of the current theoretical understanding of the dynamic structure factor of stiff polymers in semidilute solution based on the wormlike chain (WLC) model. We extend previous work by computing exact numerical coefficients and an expression for the dynamic mean square displacement (MSD) of a free polymer and compare various common approximations for the hydrodynamic interactions, which need to be treated accurately if one wants to extract quantitative estimates for model parameters from experimental data. A recent controversy about the initial slope of the dynamic structure factor is thereby resolved. To account for the interactions of the polymer with a surrounding (sticky) polymer solution, we analyze an extension of the WLC model, the glassy wormlike chain (GWLC), which predicts near power-law and logarithmic long-time tails in the dynamic structure factor.
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.
Scalable computation of kinship and identity coefficients on large pedigrees.
Cheng, En; Elliott, Brendan; Ozsoyoglu, Z Meral
2008-01-01
With the rapidly expanding field of medical genetics and genetic counseling, genealogy information is becoming increasingly abundant. An important computation on pedigree data is the calculation of identity coefficients, which provide a complete description of the degree of relatedness of a pair of individuals. The areas of application of identity coefficients are numerous and diverse, from genetic counseling to disease tracking, and thus, the computation of identity coefficients merits special attention. However, the computation of identity coefficients is not done directly, but rather as the final step after computing a set of generalized kinship coefficients. In this paper, we first propose a novel Path-Counting Formula for calculating generalized kinship coefficients, which is motivated by Wright's path-counting method for computing the inbreeding coefficient for an individual. We then present an efficient and scalable scheme for calculating generalized kinship coefficients on large pedigrees using NodeCodes, a special encoding scheme for expediting the evaluation of queries on pedigree graph structures. We also perform experiments for evaluating the efficiency of our method, and compare it with the performance of the traditional recursive algorithm for three individuals. Experimental results demonstrate that the resulting scheme is more scalable and efficient than the traditional recursive methods for computing generalized kinship coefficients. PMID:19642266
Dynamic Instabilities in Assemblies of Molecular Motors with Finite Stiffness
NASA Astrophysics Data System (ADS)
Guérin, T.; Prost, J.; Joanny, J.-F.
2010-06-01
We propose a two-state “soft-motor” model for the collective behavior of molecular motors which takes into account both the internal motor stiffness and the periodic interaction with the filament. As in the Prandtl-Tomlinson model of tribology, the important parameter of the model is the pinning parameter, which compares the stiffness of the motors to the stiffness of the potential. The model predicts dynamic instabilities in two disconnected regions of parameter space. These parameter ranges correspond to two existing theories of motor assemblies, the rigid two-state model and the crossbridge model. The model also predicts a discontinuity of the slope of the force-velocity relation at small velocities.
The interday reliability of leg and ankle musculotendinous stiffness measures.
McLachlan, Ken A; Murphy, Aron J; Watsford, Mark L; Rees, Sven
2006-11-01
Two popular methods of assessing lower body musculotendinous stiffness include the hopping and oscillation tests. The disparity and paucity of reliability data prompted this investigation into leg musculotendinous stiffness (Kleg) and ankle musculotendinous stiffness (Kank) measures. Kleg and Kank were assessed on three separate occasions in 20 female subjects. Kleg was determined using bilateral hopping procedures conducted at 2.2 Hz and 3.2 Hz frequencies. Kank was assessed by perturbation of the subject's ankle musculotendinous unit on an instrumented calf raise apparatus at 70% of maximum isometric force (MIF). Excellent reliability was produced for all Kleg measures between all days, whereas Kank exhibited acceptable reliability after one session of familiarization. No relationship was evident between Kleg and Kank. It was concluded that no familiarization session was required for Kleg at the test frequencies and conditions tested, whereas at least one familiarization session was needed to ensure the reliable assessment of Kank. PMID:17293626
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.
Role of Mineralocorticoid Receptors in Arterial Stiffness in Human Aging
Hwang, Moon-Hyon; Yoo, Jeung-Ki; Luttrell, Meredith; Kim, Han-Kyul; Meade, Thomas H.; English, Mark; Nichols, Wilmer W.; Christou, Demetra D.
2013-01-01
Arterial stiffness, an independent predictor of cardiovascular disease, is increased in aging, but the underlying mechanisms are not completely understood. Mineralocorticoid receptors (MR) may contribute to oxidative stress and arterial stiffness in healthy older adults. To test the hypothesis that short-term MR blockade may reduce oxidative stress and improve arterial stiffness, we conducted a randomized, double blind, crossover study using the selective MR blocker Eplerenone or placebo in 23 older adults (age, 64±1 years; mean±SE) free from overt cardiovascular and other clinical disease (e.g, diabetes, renal and liver disease). In response to MR blockade, brachial and carotid blood pressure decreased (P?0.01). However, MR blockade had no effect on oxidative stress (oxidized LDL, 61.2±6.8 vs. 62.4±7.4 U/L, P=0.9; placebo vs. Eplerenone) and arterial stiffness (aortic pulse wave velocity (PWV), 9.17±1.19 vs. 8.92±1.19 m/sec, P=0.5; leg PWV, 13.45±0.45 vs. 12.81±0.47 m/sec, P=0.3; arm PWV, 11.43±0.62 vs. 11.73±0.68 m/sec, P=0.7; carotid artery compliance, 0.150±0.013 vs. 0.149±0.014 mm2/mmHg, P=0.8; distensibility, 23.1±1.8 vs. 23.3±1.7 10?3/kPa, P=0.8; ? stiffness index, 3.5±0.3 vs. 3.6±0.3, P=0.6; and augmentation index, 16.0±2.2 vs. 15.6±2.8 %, P=0.8). These results provide the first evidence that MR do not appear to contribute to oxidative stress in human aging and that short-term MR blockade does not result in reduced oxidative stress and improved arterial stiffness. PMID:23707930
Aortic-brachial stiffness mismatch and mortality in dialysis population.
Fortier, Catherine; Mac-Way, Fabrice; Desmeules, Simon; Marquis, Karine; De Serres, Sacha A; Lebel, Marcel; Boutouyrie, Pierre; Agharazii, Mohsen
2015-02-01
We hypothesized that increased aortic stiffness (central elastic artery) combined with a decrease in brachial stiffness (peripheral muscular artery) leads to the reversal of the physiological stiffness gradient (ie, mismatch), promoting end-organ damages through increased forward pressure wave transmission into the microcirculation. We, therefore, examined the effect of aortic-brachial stiffness mismatch on mortality in patients in need of dialysis. In a prospective observational study, aortic-brachial arterial stiffness mismatch (pulse wave velocity ratio) was assessed using carotid-femoral pulse wave velocity divided by carotid-radial pulse wave velocity in 310 adult patients on dialysis. After a median follow-up of 29 months, 146 (47%) deaths occurred. The hazard ratio (HR) for mortality related to PWV ratio in a Cox regression analysis was 1.43 (95% confidence interval [CI], 1.24-1.64; P<0.001 per 1 SD) and was still significant after adjustments for confounding factors, such as age, dialysis vintage, sex, cardiovascular disease, diabetes mellitus, smoking status, and weight (HR, 1.23; 95% CI: 1.02-1.49). The HRs for changes in 1 SD of augmentation index (HR, 1.35; 95% CI, 1.12-1.63), carotid-femoral pulse wave velocity (HR, 1.29; 95% CI, 1.11-1.50), and carotid-radial pulse wave velocity (HR, 0.80; 95% CI, 0.67-0.95) were statistically significant in univariate analysis, but were no longer statistically significant after adjustment for age. In conclusion, aortic-brachial arterial stiffness mismatch was strongly and independently associated with increased mortality in this dialysis population. Further studies are required to confirm these finding in lower-risk groups. PMID:25452473
Aortic diameter, wall stiffness, and wave reflection in systolic hypertension.
Mitchell, Gary F; Conlin, Paul R; Dunlap, Mark E; Lacourcière, Yves; Arnold, J Malcolm O; Ogilvie, Richard I; Neutel, Joel; Izzo, Joseph L; Pfeffer, Marc A
2008-01-01
Systolic hypertension is associated with increased pulse pressure (PP) and increased risk for adverse cardiovascular outcomes. However the pathogenesis of increased PP remains controversial. One hypothesis suggests that aortic dilatation, wall stiffening and increased pulse wave velocity result from elastin fragmentation, leading to a premature reflected pressure wave that contributes to elevated PP. An alternative hypothesis suggests that increased proximal aortic stiffness and reduced aortic diameter leads to mismatch between pressure and flow, giving rise to an increased forward pressure wave and increased PP. To evaluate these two hypotheses, we measured pulsatile hemodynamics and proximal aortic diameter directly using tonometry, ultrasound imaging, and Doppler in 167 individuals with systolic hypertension. Antihypertensive medications were withdrawn for at least 1 week before study. Patients with PP above the median (75 mm Hg) had lower aortic diameter (2.94+/-0.36 versus 3.13+/-0.28 cm, P<0.001) and higher aortic wall stiffness (elastance-wall stiffness product: 16.1+/-0.7 versus 15.7+/-0.7 ln[dyne/cm], P<0.001) with no difference in augmentation index (19.9+/-10.4 versus 17.5+/-10.0%, P=0.12). Aortic diameter and wall stiffness both increased with advancing age (P<0.001). However, an inverse relation between PP and aortic diameter remained significant (P<0.001) in models that adjusted for age, sex, height, and weight and then further adjusted for aortic wall stiffness, augmentation index, and mean arterial pressure. Among individuals with systolic hypertension, increased PP is primarily attributable to increased wall stiffness and reduced aortic diameter rather than premature wave reflection. PMID:18071054
Fractal diffusion coefficient from dynamical zeta functions
G. Cristadoro
2005-09-28
Dynamical zeta functions provide a powerful method to analyze low dimensional dynamical systems when the underlying symbolic dynamics is under control. On the other hand even simple one dimensional maps can show an intricate structure of the grammar rules that may lead to a non smooth dependence of global observable on parameters changes. A paradigmatic example is the fractal diffusion coefficient arising in a simple piecewise linear one dimensional map of the real line. Using the Baladi-Ruelle generalization of the Milnor-Thurnston kneading determinant we provide the exact dynamical zeta function for such a map and compute the diffusion coefficient from its smallest zero.
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.
Uemura, Hirokazu; Katsuura-Kamano, Sakurako; Yamaguchi, Miwa; Nakamoto, Mariko; Hiyoshi, Mineyoshi; Arisawa, Kokichi
2014-10-28
Studies on the associations of dietary Ca and vitamin D intakes with arterial stiffness are scarce. In the present study, these associations were evaluated in Japanese men. Data from a total of 535 eligible men, aged 35-69 years, who participated in the baseline survey of a cohort study in Tokushima Prefecture, Japan, and underwent brachial-ankle pulse wave velocity (ba-PWV) measurements were analysed. ba-PWV is a measure of arterial stiffness and is recognised as a marker of atherosclerotic vascular damage. Information regarding the cohort's lifestyle characteristics including dietary behaviour over the past year was obtained from a structured self-administered questionnaire. Dietary Ca and vitamin D intakes were adjusted for total energy intake using the residual method and divided into quartiles; the highest quartile was used as the reference. General linear models were used to evaluate the associations between dietary Ca and vitamin D intakes and ba-PWV values adjusted for probable covariates. The association between dietary Ca intake and ba-PWV was further evaluated using similar general linear models stratified by dietary vitamin D intake (median or below/above median). Dietary Ca intake was found to be significantly inversely associated with ba-PWV after adjusting for probable covariates (P for trend = 0·020). However, no such association was observed between dietary vitamin D intake and ba-PWV. The inverse association between dietary Ca intake and ba-PWV was striking in subjects with higher dietary vitamin D intake. However, no association was found in subjects with lower dietary vitamin D intake. These results indicate that adequate dietary Ca and vitamin D intakes may be protective against the development of arterial stiffness in Japanese men. PMID:25192171
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.
Use of Structure Coefficients in Published Multiple Regression Articles: &bgr; is not Enough
Troy Courville; Bruce Thompson
2001-01-01
The importance of interpreting structure coefficients throughout the General Linear Model (GLM) is widely accepted. However, regression researchers too infrequently consult regression structure coefficients to augment their interpretations. The authors reviewed articles published in the Journal of Applied Psychology to determine how interpretations might have differed if standardized regression coefficients and structure coefficients (or else bivariate rs of predictors with
Matthijs Joost Warrens
2008-01-01
In data analysis, an important role is played by similarity coefficients. A similarity coefficient is a measure of resemblance or association of two entities or variables. Similarity coefficients for binary data are used, for example, in biological ecology for measuring the degree of coexistence between two species type over different locations, or in psychology for a 2×2 reliability study where
Dara Childs; Keith Hale
1994-01-01
A facility and apparatus are described which determine stiffness, damping, and added-mass rotordynamic coefficients plus steady-state operating characteristics of high speed hydrostatic journal bearings. The apparatus has a current top speed of 29,800 rpm with a bearing diameter of 7.62 cm (3 in.). Purified warm water, 55 C (130 F), is used as a test fluid to achieve elevated Reynolds
[Anesthetic management for thymectomy in a patient with stiff-person syndrome].
Nakamura, Taketo; Oda, Yutaka; Matsushita, Mitsuji; Mori, Takashi; Ikeshita, Kazutoshi; Asada, Akira
2007-10-01
Stiff-person syndrome is an autoimmune disease characterized by muscle rigidity accompanied by decreased respiratory function. We report a patient with this syndrome who underwent thymectomy under general anesthesia. A 79-year-old woman complaining of increasing muscle rigidity over the past four months was transferred to this hospital. Marked speech disturbance and dysphagia were observed on admission. The diagnosis of stiff-person syndrome was made based on an increase in serum anti-glutamic acid decarboxylase antibody level and thymoma in the anterior mediastinum. Following alleviation of muscle rigidity by high-dose gamma-globulin, thymectomy was scheduled. General anesthesia was given with propofol, fentanyl and epidural ropivacaine. Propofol was continuously infused to maintain BIS below 60 and vecuronium was intermittently administered when muscle contraction was observed in response to electrical stimulation of the ulnar nerve. Despite full recovery of muscle contractility following surgery, tidal volume was too low to remove the tracheal tube, and mechanical ventilation was continued in ICU. One hour after admission to ICU, the tracheal tube was removed, with no marked changes in respiratory condition thereafter. Since many anesthetics are respiratory suppressants that can delay the recovery of respiratory function, careful monitoring of respiratory condition is required postoperatively. PMID:17966628
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
Stiffness gradients in vascular bundles of the palm Washingtonia robusta
Rüggeberg, Markus; Speck, Thomas; Paris, Oskar; Lapierre, Catherine; Pollet, Brigitte; Koch, Gerald; Burgert, Ingo
2008-01-01
Palms can grow at sites exposed to high winds experiencing large dynamic wind and gust loads. Their stems represent a system of stiff fibrous elements embedded in the soft parenchymatous tissue. The proper design of the interface of the stiffening elements and the parenchyma is crucial for the functioning of the stem. The strategy of the palm to compromise between stiff fibre caps and the soft parenchymatous tissue may serve as a model system for avoiding stress discontinuities in inhomogeneous and anisotropic fibre-reinforced composite materials. We investigated the mechanical, structural and biochemical properties of the fibre caps of the palm Washingtonia robusta at different levels of hierarchy with high spatial resolution. A gradual decrease in stiffness across the fibre cap towards the surrounding parenchymatous tissue was observed. Structural adaptations at the tissue level were found in terms of changes in cell cross sections and cell wall thickness. At the cell wall level, gradients across the fibre cap were found in the degree of orientation of the microfibrils and in the lignin level and composition. The impact of these structural variations in the local material stiffness distribution is discussed. PMID:18595839
Influence of Passive Stiffness of Hamstrings on Postural Stability
Kuszewski, Micha?; Gnat, Rafa?; Sobota, Grzegorz; My?liwiec, 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
Structure, Stiffness and Substates of the Dickerson-Drew Dodecamer
Dršata, Tomáš; Pérez, Alberto; Orozco, Modesto; Morozov, Alexandre V.; Šponer, Ji??; Lankaš, Filip
2013-01-01
The Dickerson–Drew dodecamer (DD) d-[CGCGAATTCGCG]2 is a prototypic B-DNA molecule whose sequence-specific structure and dynamics have been investigated by many experimental and computational studies. Here, we present an analysis of DD properties based on extensive atomistic molecular dynamics (MD) simulations using different ionic conditions and water models. The 0.6–2.4-µs-long MD trajectories are compared to modern crystallographic and NMR data. In the simulations, the duplex ends can adopt an alternative base-pairing, which influences the oligomer structure. A clear relationship between the BI/BII backbone substates and the basepair step conformation has been identified, extending previous findings and exposing an interesting structural polymorphism in the helix. For a given end pairing, distributions of the basepair step coordinates can be decomposed into Gaussian-like components associated with the BI/BII backbone states. The nonlocal stiffness matrices for a rigid-base mechanical model of DD are reported for the first time, suggesting salient stiffness features of the central A-tract. The Riemann distance and Kullback–Leibler divergence are used for stiffness matrix comparison. The basic structural parameters converge very well within 300 ns, convergence of the BI/BII populations and stiffness matrices is less sharp. Our work presents new findings about the DD structural dynamics, mechanical properties, and the coupling between basepair and backbone configurations, including their statistical reliability. The results may also be useful for optimizing future force fields for DNA. PMID:23976886
Magnetorheological brush - a soft structure with highly tuneable stiffness.
Huang, Xiao; Mohla, Akshi; Hong, Wei; Bastawros, Ashraf F; Feng, Xi-Qiao
2014-03-14
By combining the field-stiffening effect of magnetorheological (MR) elastomers and the Euler buckling mechanism, we developed a brush-like magneto-active structure with highly tuneable stiffness. When the applied mechanical load is within a certain range, the effective stiffness of the structure can be tuned by several orders of magnitude with the applied magnetic field. The performance of the structure and its dependence on various synthesis parameters, such as the curing field and filler concentration, were investigated experimentally. It is found that the increase in the critical load for buckling is more than the contribution from the stiffening of the MR elastomer. To unravel the relationship between the stiffness increase and the applied field, a theoretical model with coupled mechanical deformation and magnetic field is established. The prediction of the model agrees well with experimental results. The theory may also be used to model the behaviour of other similar materials, such as MR gels. The MR brush developed in this research holds promise for potential applications in smart structures or devices that require mechanical stiffness to be tuneable in a relatively large range. As the amplification mechanism is independent of the base material, it could be used in conjunction with emerging MR materials for further enhanced performance. PMID:24652105
Accelerated Stochastic Simulation of the Stiff Enzyme-Substrate Reaction
Cao, Yang
1 Accelerated Stochastic Simulation of the Stiff Enzyme-Substrate Reaction Yang Cao a) Dept, Santa Barbara, Santa Barbara, CA 93106 Abstract: The enzyme-catalyzed conversion of a substrate this process, the intermediate enzyme-substrate complex is usually much more likely to decay into its original
Hyperbolic conservation laws with stiff relaxation terms and entropy
Gui-Qiang Chen; C. David Levermore; Tai-Ping Liu
1994-01-01
We study the limiting behavior of systems of hyperbolic conservation lawswith stiff relaxation terms. Reduced systems, inviscid and viscous local conservationlaws, and weakly nonlinear limits are derived through asymptotic expansions.An entropy condition is introduced for N \\\\Theta N systems that ensuresthe hyperbolicity of the reduced inviscid system. The resulting characteristicspeeds are shown to be interlaced with those of the original
Simultaneously high stiffness and damping in nanoengineered microtruss composites.
Meaud, Julien; Sain, Trisha; Yeom, Bongjun; Park, Sei Jin; Shoultz, Anna Brieland; Hulbert, Gregory; Ma, Zheng-Dong; Kotov, Nicholas A; Hart, A John; Arruda, Ellen M; Waas, Anthony M
2014-04-22
Materials combining high stiffness and mechanical energy dissipation are needed in automotive, aviation, construction, and other technologies where structural elements are exposed to dynamic loads. In this paper we demonstrate that a judicious combination of carbon nanotube engineered trusses held in a dissipative polymer can lead to a composite material that simultaneously exhibits both high stiffness and damping. Indeed, the combination of stiffness and damping that is reported is quite high in any single monolithic material. Carbon nanotube (CNT) microstructures grown in a novel 3D truss topology form the backbone of these nanocomposites. The CNT trusses are coated by ceramics and by a nanostructured polymer film assembled using the layer-by-layer technique. The crevices of the trusses are then filled with soft polyurethane. Each constituent of the composite is accurately modeled, and these models are used to guide the manufacturing process, in particular the choice of the backbone topology and the optimization of the mechanical properties of the constituent materials. The resulting composite exhibits much higher stiffness (80 times) and similar damping (specific damping capacity of 0.8) compared to the polymer. Our work is a step forward in implementing the concept of materials by design across multiple length scales. PMID:24620996
Substrata Mechanical Stiffness Can Regulate Adhesion of Viable Bacteria
Van Vliet, Krystyn J.
Substrata Mechanical Stiffness Can Regulate Adhesion of Viable Bacteria Jenny A. Lichter,, M. Todd, 2008 The competing mechanisms that regulate adhesion of bacteria to surfaces and subsequent biofilm and hospital-acquired infections due to bacteria, there is considerable interest in better understanding
GEOMETRIC STIFFNESS AND STABILITY OF RIGID BODY MODES
H. El-Absy; A. A. Shabana
1997-01-01
The objective of this study is to examine the effect of geometric stiffness forces on the stability of elastic and rigid body modes. A simple rotating beam model is used to demonstrate the effect of axial forces and dynamic coupling between the modes of displacement on the rigid body motion. The effect of longitudinal deformation due to bending is systematically
Human arm stiffness characteristics during the maintenance of posture
T. Flash; F. Mussa-Ivaldi
1990-01-01
When the hand is displaced from an equilibrium position, the muscles generate elastic forces to restore the original posture. In a previous study, Mussa-Ivaldi et al. (1985) have measured and characterized the field of elastic forces associated with hand posture in the horizontal plane. Hand stiffness which describes the relation between force and displacement vectors in the vicinity of equilibrium
Torsion Stiffness of a Protein Pair Determined by Magnetic Particles
Janssen, X.J.A.; van Noorloos, J.M.; Jacob, A.; van IJzendoorn, L.J.; de Jong, A.M.; Prins, M.W.J.
2011-01-01
We demonstrate the ability to measure torsion stiffness of a protein complex by applying a controlled torque on a magnetic particle. As a model system we use protein G bound to an IgG antibody. The protein pair is held between a magnetic particle and a polystyrene substrate. The angular orientation of the magnetic particle shows an oscillating behavior upon application of a rotating magnetic field. The amplitude of the oscillation increases with a decreasing surface coverage of antibodies on the substrate and with an increasing magnitude of the applied field. For decreasing antibody coverage, the torsion spring constant converges to a minimum value of 1.5 × 103 pN·nm/rad that corresponds to a torsion modulus of 4.5 × 104 pN·nm2. This torsion stiffness is an upper limit for the molecular bond between the particle and the surface that is tentatively assigned to a single protein G–IgG protein pair. This assignment is supported by interpreting the measured stiffness with a simple mechanical model that predicts a two orders of magnitude larger stiffness for the protein G–IgG complex than values found for micrometer length dsDNA. This we understand from the structural properties of the molecules, i.e., DNA is a long and flexible chain-like molecule, whereas the antibody-antigen couple is orders of magnitude smaller and more globular in shape due to the folding of the molecules. PMID:21539795
Verifying Stiffness Parameters Of Filament-Wound Cylinders
NASA Technical Reports Server (NTRS)
Verderaime, V.; Rheinfurth, M.
1994-01-01
Predicted engineering stiffness parameters of filament-wound composite-material cylinders verified with respect to experimental data, by use of equations developed straightforwardly from applicable formulation of Hooke's law. Equations derived in engineering study of filament-wound rocket-motor cases, also applicable to other cylindrical pressure vessels made of orthotropic materials.
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
Stiffness, not inertial coupling, determines path curvature of wrist motions.
Charles, Steven K; Hogan, Neville
2012-02-01
When humans rotate their wrist in flexion-extension, radial-ulnar deviation, and combinations, the resulting paths (like the path of a laser pointer on a screen) exhibit a distinctive pattern of curvature. In this report we show that the passive stiffness of the wrist is sufficient to account for this pattern. Simulating the dynamics of wrist rotations using a demonstrably realistic model under a variety of conditions, we show that wrist stiffness can explain all characteristics of the observed pattern of curvature. We also provide evidence against other possible causes. We further demonstrate that the phenomenon is robust against variations in human wrist parameters (inertia, damping, and stiffness) and choice of model inputs. Our findings explain two previously observed phenomena: why faster wrist rotations exhibit more curvature and why path curvature rotates with pronation-supination of the forearm. Our results imply that, as in reaching, path straightness is a goal in the planning and control of wrist rotations. This requires humans to predict and compensate for wrist dynamics, but, unlike reaching, nonlinear inertial coupling (e.g., Coriolis acceleration) is insignificant. The dominant term to be compensated is wrist stiffness. PMID:22131378
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.
Stiffness of cancer cells measured with an AFM indentation method.
Hayashi, Kozaburo; Iwata, Mayumi
2015-09-01
The stiffness of cancer cells and its changes during metastasis are very important for understanding the pathophysiology of cancer cells and the mechanisms of metastasis of cancer. As the first step of the studies on the mechanics of cancer cells during metastasis, we determined the elasticity and stiffness of cancer cells with an indentation method using an atomic force microscope (AFM), and compared with those of normal cells. In most of the past AFM studies, Young?s elastic moduli of cells have been calculated from force-indentation data using Hertzian model. As this model is based on several important assumptions including infinitesimal strain and Hooke?s linear stress-strain law, in the exact sense it cannot be applied to cells that deform very largely and nonlinearly. To overcome this problem, we previously proposed an equation F=a[exp(b?)-1] to describe relations between force (F) and indentation (?), where a and b are parameters relating with cellular stiffness. In the present study, we applied this method to cancer cells instead of Young?s elastic modulus. The conclusions obtained are: 1) AFM indentation test data of cancer cells can be very well described by the above equation, 2) cancer cells are softer than normal cells, and 3) there are no significant locational differences in the stiffness of cancer cells between the central and the peripheral regions. These methods and results are useful for studying the mechanics of cancer cells and the mechanisms of metastasis. PMID:26004036
Stiffness and damping characteristics of aluminum in creep
A. Berkovits
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
Variable stiffness property study on shape memory polymer composite tube
Yijin Chen; Jian Sun; Yanju Liu; Jinsong Leng
2012-01-01
As a typical smart material, shape memory polymers (SMPs) have the capability of variable stiffness in response to external stimuli, such as heat, electricity, magnetism and solvents. In this research, a shape memory polymer composite (SMPC) tube composed of multi-layered filament wound structures is investigated. The SMPC tube possesses considerable flexibility under high temperature and rigidity under low temperature. Significant
Exploiting Passive Dynamics with Variable Stiffness Actuation in Robot Brachiation
Vijayakumar, Sethu
such as energy storage in explosive movements from a viewpoint of performance improvement. Braun et al. [3] have focus on the passive control strategy with variable stiffness actuation for swing movements.nakanishi@ed.ac.uk, sethu.vijayakumar@ed.ac.uk Abstract--This paper explores a passive control strategy with variable
The influence of musculotendinous stiffness on drop jump performance.
Walshe, A D; Wilson, G J
1997-04-01
This study investigated the relationship between musculotendinous stiffness and the ability to perform dynamic stretch-shorten cycle actions involving a range of eccentric loads. Twenty trained male subjects performed a series of quasi-static muscular actions in a supine leg press position, during which a brief perturbation was applied. The resulting damped oscillations allowed the estimation of each subject's maximal musculotendinous stiffness (k) for the lower body musculature. All subjects also performed a countermovement jump (CMJ) and a series of drop jumps (DJs) from heights of 20, 40, 60, 80, and 100 cm. When the jump heights of the nine most compliant (mean k = 11.4 +/- 2.7 kNxm-1) and nine stiffest (mean k = 20.5 +/- 2.5 kNxm-1) subjects were compared the stiff subjects demonstrated significantly poorer capacity to perform under the highest (DJ80 and DJ100) eccentric loading conditions. It was hypothesised that the relatively greater forces transmitted from the skeletal system to the musculature of the stiff subjects reduced their ability to attenuate the higher eccentric loads due to less effective contractile dynamics and greater levels of reflex induced inhibition. PMID:9140666
Stiff man syndrome: Clinical and laboratory findings in eight patients
H.-M. Meinck; K. Ricker; P.-J. Hülser; E. Schmid; J. Peiffer; M. Solimena
1994-01-01
The clinical, biochemical, neuroimaging and neurophysiological findings of eight patients with stiff man syndroms (SMS) [four of six being tested with autoantibodies against glutamic acid decarboxylase (GAD)] are presented. In two patients (one GAD-positive, one GAD-negative), transient oculomotor disturbances suggested progressive encephalomyelitis with rigidity and myoclonus (PERM) as differential diagnosis. The catalogue of characteristic clinical symptoms of SMS is extended
Haptic Rendering of Drilling into Femur Bone with Graded Stiffness
Jang Ho Cho; Hoeryong Jung; Kyungno Lee; Doo Yong Lee; Hyung Soo Ahn
2007-01-01
This paper presents haptic rendering method of drilling into femur bone with graded stiffness. Volume rendering is preferred than surface rendering in drilling or burr simulation because the volume rendering can contain information such as density and rigidity of each voxel. However, it is difficult to implement real-time graphics and haptic rendering because of the large computational workload. Therefore, we
Determination of the stiffness of rolling kinematic pairs of manipulators
Przemys?aw Szumi?ski
2007-01-01
A method of determination of the radial and axial stiffness of rolling bearings and rolling kinematic pairs as a function of the external load and the kinematics of motion has been presented. In this method, an influence of the distribution of rolling elements during the bearing raceway motion (with respect to the direction the resultant vector of the radial load
An Ultrawideband Radar Based Pulse Sensor for Arterial Stiffness Measurement
Teh-Ho Tao; Shin-Jen Hu; Jla-Hung Peng; Su-Chen Kuo
2007-01-01
A novel pulse sensor based on ultrawideband (UWB) radar to detect the arterial vessel movements on various sites on human body without applying external pressure on the arterial vessel was designed and evaluated for aortic stiffness measurement. The UWB pulse sensor was evaluated for its functional performance and human study was carried out to validate the UWB sensor as a
On implicit Taylor series methods for stiff ODEs
Kirlinger, G. (Technische Univ., Vienna (Austria). Inst. fuer Angewandte und Numerische Mathematik); Corliss, G.F. (Argonne National Lab., IL (United States))
1991-01-01
Several versions of implicit Taylor series methods (ITSM) are presented and evaluated. Criteria for the approximate solution of ODEs via ITSM are given. Some ideas, motivations, and remarks on the inclusion of the solution of stiff ODEs are outlined. 25 refs., 3 figs.
On implicit Taylor series methods for stiff ODEs
Kirlinger, G. [Technische Univ., Vienna (Austria). Inst. fuer Angewandte und Numerische Mathematik; Corliss, G.F. [Argonne National Lab., IL (United States)
1991-12-31
Several versions of implicit Taylor series methods (ITSM) are presented and evaluated. Criteria for the approximate solution of ODEs via ITSM are given. Some ideas, motivations, and remarks on the inclusion of the solution of stiff ODEs are outlined. 25 refs., 3 figs.
Massively parallel computation of stiff propagating combustion fronts
Marc Garbey; Damien Tromeur-Dervout
1997-01-01
Gas combustion, solid combustion as well as frontal polymerization are characterized by stiff fronts that propagate with nonlinear dynamics. The multiple-scale phenomena under consideration lead to very intense computations that require parallel computing in order to reduce the elapsed time of the computation. We develop a methodology to build on the MIMD architecture a parallel numerical method based on the
Electromagnetic Field in Some Anisotropic Stiff Fluid Universes
Pimentel L O
1995-07-25
The electromagnetic field is studied in a family of exact solutions of the Einstein equations whose material content is a perfect fluid with stiff equation of state (p = $\\epsilon $ ). The field equations are solved exactly for several members of the family.
Quaternion-based impedance with nondiagonal stiffness for robot manipulators
Fabrizio Caccavale; Bruno Siciliano; Luigi Villani
1998-01-01
In this paper an energy-based argument is used to derive the dynamic equation of a mechanical impedance at the end effector of a robot manipulator, both for its translational part and for its rotational part. The adoption of unit quaternions to describe orientation displacements leads to a geometrically consistent definition of the stiffness in the impedance equation. Remarkably, off-diagonal elements
Joint stiffness identification of six-revolute industrial serial robots
Claire Dumas; Stéphane Caro; Sébastien Garnier; Benoît Furet
2011-01-01
Although robots tend to be as competitive as CNC machines for some operations, they are not yet widely used for machining operations. This may be due to the lack of certain technical information that is required for satisfactory machining operation. For instance, it is very difficult to get information about the stiffness of industrial robots from robot manufacturers. As a
On the development of planar actuators for variable stiffness devices
NASA Astrophysics Data System (ADS)
Henke, Markus; Gerlach, Gerald
2013-04-01
This contribution describes the development, the potential and the limitations of planar actuators for controlling bending devices with variable stiffness. Such structures are supposed to be components of new smart, self-sensing and -controlling composite materials for lightweight constructions. To realize a proper stiffness control, it is necessary to develop reliable actuators with high actuation capabilities based on smart materials. Several actuator designs driven by electroactive polymers (EAPs) are presented and discussed regarding to their applicability in such structures. To investigate the actuators, variable-flexural stiffness devices based on the control of its area moment of inertia were developed. The devices consist of a multi-layer stack of thin, individual plates. Stiffness variation is caused by planar actuators which control the sliding behavior between the layers by form closure structures. Previous investigations have shown that actuators with high actuation potential are needed to ensure reliable connections between the layers. For that reason, two kinds of EAPs Danfoss PolyPower and VHB 4905 by 3M, have been studied as driving unit. These EAP-driven actuators will be compared based on experimental measurements and finite element analyses.
Design of a Stiff Steerable Grasper for Sinus Surgery
Webster III, Robert James
Background With the advent of endoscopic sinus surgery in the late 1980's [1], a completely new surgical of the sinuses. Today, functional endoscopic sinus surgery (FESS) is commonly used to improve the sinusesDesign of a Stiff Steerable Grasper for Sinus Surgery Andria A. Remirez, Ray A. Lathrop, Paul T
Arthroscopic Treatment of Posttraumatic Elbow Pain and Stiffness
Laura A. Timmerman; James R. Andrews
1994-01-01
Nineteen consecutive cases of posttraumatic arthrofi brosis of the elbow secondary to a fracture or fracture- dislocation and treated with arthroscopic debridement and manipulation were retrospectively reviewed. All of the patients had pain and stiffness in their elbows, and all had failed a conservative therapy program. All 19 patients were followed postoperatively for an average of 29 months (range, 12
Vascular calcification: A stiff challenge for the nephrologist
DAVID GOLDSMITH; EBERHARD RITZ; ADRIAN COVIC
2004-01-01
Vascular calcification: A stiff challenge for the nephrologists—Does preventing bone disease cause arterial disease? There has been an explosion of interest in vascular calcification in the last 5 years. Four key “germinal” findings have fallen onto very fertile soil. First, on the background of an increasing cardiovascular disease burden it has been found that at least cross-sectionally, and in a
Stiffness mapping of compliant parallel mechanisms in a serial arrangement
Florida, University of
Stiffness mapping of compliant parallel mechanisms in a serial arrangement Hyun K. Jung a , Carl D of a mechanism having two compliant parallel mechanisms in a serial arrange- ment. A derivative of the wrench. It is shown that the resultant compliance of two compliant parallel mechanisms that are serially arranged
Loss coefficient correlation for wet-cooling tower fills
Johannes C. Kloppers; Detlev G. Kröger
2003-01-01
Loss coefficient correlations given in the literature for wet-cooling tower fills are relatively simple and generally do not represent the pressure drop accurately over a wide range of operational conditions. A new form of empirical equation is proposed that correlates fill loss coefficient data more effectively when compared to other forms of empirical equations commonly found in the literature.
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;…
An Evolving Scale-free Network with Large Clustering Coefficient
Peihua Fu; Kun Liao
2006-01-01
Preferential attachment is generally regarded as the best mechanism to form scale-free networks. However, the simulated network has a much smaller clustering coefficient, while many networks in the real world, such as movie actors' collaboration and co-authorship networks, have a high clustering coefficient. So we develop the relatively preferential attachment (RPA) method which considers preferential attachment as well as the
Drag Coefficient of Hexadecane Particles
NASA Astrophysics Data System (ADS)
Nakao, Yoshinobu; Hishida, Makoto; Kajimoto, Sadaaki; Tanaka, Gaku
This paper deals with the drag coefficient of solidified hexadecane particles and their free rising velocity in liquid. The drag coefficient was experimentally investigated in Reynolds number range of about 40-300. The present experimental results are summarized in the following; (1) the drag coefficient of solidified hexadecane particles formed in liquid coolant by direct contact cooling is higher than that of a smooth surface sphere, this high drag coefficient seems to be attributed to the non-smooth surface of the solidified hexadecane particles, (2) experimental correlation for the drag coefficient of the solidified hexadecane particles was proposed, (3 ) the measured rising velocity of the solidified hexadecane particle agrees well with the calculated one, (4) the drag coefficients of hexadecane particles that were made by pouring hexadecane liquid into a solid hollow sphere agreed well with the drag coefficient of smooth surface sphere.
Predictors of Postoperative Finger Stiffness in Unstable Proximal Phalangeal Fractures
Onishi, Tadanobu; Shimizu, Takamasa; Fujitani, Ryotaro; Shigematsu, Koji; Tanaka, Yasuhito
2015-01-01
Background: The purpose of this study was to determine the risk factors for postoperative finger stiffness after open reduction and internal fixation of unstable proximal phalangeal fractures using a low-profile plate and/or screw system. We hypothesized that dorsal plate placement is a risk factor for postoperative finger stiffness. Methods: Seventy consecutive patients (50 men, 20 women; average age, 40 years) with 75 unstable proximal phalangeal fractures were treated with titanium plates and/or screws and evaluated at a minimum follow-up of 1 year. Thirty-six comminuted fractures and 24 intra-articular fractures were included, and 16 fractures had associated soft-tissue injuries. Plate fixation was performed in 59 fractures, and the remaining 16 were fixed with screws only. The implants were placed in a dorsal location in 33 fractures and in a lateral or volar location in 42 fractures. Finger stiffness was defined as a total active range of finger motion <80% for the treated finger. Univariate and multivariate analyses were performed on 8 variables: patient characteristics (age and sex), fracture characteristics (fracture comminution, joint involvement, and associated soft-tissue injury), and surgical characteristics (type and location of implants and removal of the implants). Results: Postoperative finger stiffness occurred in 38 fractures. The multivariate analysis indicated that plate fixation (odds ratio, 5.9; 95% confidence interval, 1.5–24.0; P = 0.01) and dorsal placement (odds ratio, 3.0; 95% confidence interval, 1.1–8.3; P = 0.03) were independent risk factors for finger stiffness. Conclusion: We recommend the use of screw fixation as much as possible for unstable proximal phalangeal fractures using a midlateral approach.
An acoustic startle alters knee joint stiffness and neuromuscular control.
DeAngelis, A I; Needle, A R; Kaminski, T W; Royer, T R; Knight, C A; Swanik, C B
2015-08-01
Growing evidence suggests that the nervous system contributes to non-contact knee ligament injury, but limited evidence has measured the effect of extrinsic events on joint stability. Following unanticipated events, the startle reflex leads to universal stiffening of the limbs, but no studies have investigated how an acoustic startle influences knee stiffness and muscle activation during a dynamic knee perturbation. Thirty-six individuals were tested for knee stiffness and muscle activation of the quadriceps and hamstrings. Subjects were seated and instructed to resist a 40-degree knee flexion perturbation from a relaxed state. During some trials, an acoustic startle (50?ms, 1000?Hz, 100?dB) was applied 100?ms prior to the perturbation. Knee stiffness, muscle amplitude, and timing were quantified across time, muscle, and startle conditions. The acoustic startle increased short-range (no startle: 0.044?±?0.011?N·m/deg/kg; average startle: 0.047?±?0.01?N·m/deg/kg) and total knee stiffness (no startle: 0.036?±?0.01?N·m/deg/kg; first startle 0.027?±?0.02?N·m/deg/kg). Additionally, the startle contributed to decreased [vastus medialis (VM): 13.76?±?33.6%; vastus lateralis (VL): 6.72?±?37.4%] but earlier (VM: 0.133?±?0.17?s; VL: 0.124?±?0.17?s) activation of the quadriceps muscles. The results of this study indicate that the startle response can significantly disrupt knee stiffness regulation required to maintain joint stability. Further studies should explore the role of unanticipated events on unintentional injury. PMID:25212407
Wrinkling of Stiff Films on Stretched Compliant Films: Experimental and Theoretical Studies
Yang, Yi
2013-12-06
Wrinkling of stiff film on semi-infinite compliant substrates has attracted attentions recently due to its important applications in stretchable electronics and micro-pattern metrology. However, wrinkling of a stiff film on a compliant thin film...
jamSheets: Thin Interfaces with Tunable Stiffness Enabled by Layer Jamming
Ou, Jifei
This works introduces layer jamming as an enabling technology for designing deformable, stiffness-tunable, thin sheet interfaces. Interfaces that exhibit tunable stiffness properties can yield dynamic haptic feedback and ...
Zero finite-temperature charge stiffness within the half-filled 1D Hubbard model
Carmelo, J.M.P., E-mail: carmelo@fisica.uminho.pt [Center and Department of Physics, University of Minho, Campus Gualtar, P-4710-057 Braga (Portugal) [Center and Department of Physics, University of Minho, Campus Gualtar, P-4710-057 Braga (Portugal); Beijing Computational Science Research Center, Beijing 100084 (China); Institut für Theoretische Physik III, Universität Stuttgart, D-70550 Stuttgart (Germany); Gu, Shi-Jian [Beijing Computational Science Research Center, Beijing 100084 (China) [Beijing Computational Science Research Center, Beijing 100084 (China); Department of Physics and ITP, Chinese University of Hong Kong, Hong Kong (China); Sacramento, P.D. [CFIF, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal) [CFIF, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Beijing Computational Science Research Center, Beijing 100084 (China)
2013-12-15
Even though the one-dimensional (1D) Hubbard model is solvable by the Bethe ansatz, at half-filling its finite-temperature T>0 transport properties remain poorly understood. In this paper we combine that solution with symmetry to show that within that prominent T=0 1D insulator the charge stiffness D(T) vanishes for T>0 and finite values of the on-site repulsion U in the thermodynamic limit. This result is exact and clarifies a long-standing open problem. It rules out that at half-filling the model is an ideal conductor in the thermodynamic limit. Whether at finite T and U>0 it is an ideal insulator or a normal resistor remains an open question. That at half-filling the charge stiffness is finite at U=0 and vanishes for U>0 is found to result from a general transition from a conductor to an insulator or resistor occurring at U=U{sub c}=0 for all finite temperatures T>0. (At T=0 such a transition is the quantum metal to Mott–Hubbard-insulator transition.) The interplay of the ?-spin SU(2) symmetry with the hidden U(1) symmetry beyond SO(4) is found to play a central role in the unusual finite-temperature charge transport properties of the 1D half-filled Hubbard model. -- Highlights: •The charge stiffness of the half-filled 1D Hubbard model is evaluated. •Its value is controlled by the model symmetry operator algebras. •We find that there is no charge ballistic transport at finite temperatures T>0. •The hidden U(1) symmetry controls the U=0 phase transition for T>0.
Leloup, Arthur J A; Fransen, Paul; Van Hove, Cor E; Demolder, Marc; De Keulenaer, Gilles W; Schrijvers, Dorien M
2014-07-01
Arterial stiffening is the root cause of a range of cardiovascular complications, including myocardial infarction, left ventricular hypertrophy, stroke, renal failure, dementia, and death, and a hallmark of the aging process. The most important in vivo parameter of arterial stiffness is pulse wave velocity (PWV). Clinically, PWV is determined noninvasively using applanation tonometry. Unlike the clinical value of arterial stiffness and PWV, techniques to determine PWV in mice are scarce. The only way to determine aortic PWV noninvasively in the mouse is by using ultrasound echo Doppler velocimetry. It is a fast, efficient, and accurate technique, but the required tools are expensive and technically complex. Here, we describe the development and validation of a novel technique to assess carotid-femoral PWV noninvasively in mice. This technique is based on applanation tonometry as used clinically. We were able to establish a reproducible reference value in wild-type mice (3.96±0.05 m/s) and to detect altered carotid-femoral PWV values in endothelial nitric oxide synthase knockout mice (4.66±0.05 m/s; P<0.001 compared with control), and in mice sedated with sodium pentobarbital (2.89±0.17 m/s; P<0.001 compared with control). Also, carotid-femoral PWV was pharmacologically modulated and measured in a longitudinal experiment with endothelial nitric oxide synthase knockout mice to demonstrate the applicability of this technique. In general, applanation tonometry can be used to measure carotid-femoral PWV noninvasively in mice. The experimental setup is simple, and the technical requirements are basic, making this technique readily implementable in any mouse model-based research facility interested in arterial stiffness. PMID:24752435
Statistical modeling of DCT coefficients for audio
Cuiping Wang; Li Guo; Yifang Wei; Yujie Wang
2010-01-01
Based on the sharp-peak and heavy-tail of statistical distribution of discrete cosine transform (DCT) coefficients for audio, generalized Gaussian distribution (GGD) and alpha-stable distribution are usually employed as modeling tools. In this paper, the Kullback-Leibler Divergence is applied to measure the difference between modeling result and the true distribution, and the experiment results show that compared with alpha-stable distribution, the
Cè, 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
Moo-Yong Rhee; Sang-Hoon Na; Young-Kwon Kim; Myoung-Mook Lee; Hae-Young Kim
2007-01-01
Background: Although the acute increase of arterial stiffness and blood pressure (BP) after cigarette smoking in healthy smokers is considered a possible mechanism of increased cardiovascular risk, the acute effect of smoking on arterial stiffness in hypertensive smokers is unknown. We investigated the acute effects of cigarette smoking on arterial stiffness and BP in hypertensive male smokers.Methods: Heart rate (HR),
Absence of Age-Related Increase in Central Arterial Stiffness in Physically Active Women
Hirofumi Tanaka; Christopher A. DeSouza; Douglas R. Seals
Increased arterial stiffness is thought to contribute to the increased incidence of cardiovascular disease with age. Little, however, is known about the influence of aging on central and peripheral arterial stiffness in females. Moreover, it is unknown whether physical activity status influences age-related increases in arterial stiffness in females. Arterial pulse wave velocity (PWV) and augmentation index (AI, applanation tonometry)
ORIGINAL PAPER The decreasing radial wood stiffness pattern of some tropical
Paris-Sud XI, Université de
This study examines the radial trend in wood stiffness of tropical rainforest trees. The objectiveORIGINAL PAPER The decreasing radial wood stiffness pattern of some tropical trees growing. Keywords Tropical trees . Growth strategy. Wood stiffness . Juvenile wood 1 Introduction In addition
A new pre-loaded membrane geometric stiffness matrix with full rigid body capabilities
Paul A. Bosela; D. R. Ludwiczak
1996-01-01
Space structures, due to economic considerations, must be light-weight. Accurate prediction of the natural frequencies and mode shapes is critical for determining the structural adequacy of components, and designing a control system. The total stiffness of a member, in many cases, includes both the elastic stiffness of the material as well as additional geometric stiffness due to pre-load (initial stress
Monsak Pimsarn; Kazem Kazerounian
2002-01-01
This paper presents a new method, pseudo-interference stiffness estimation (PISE), for evaluating the equivalent mesh stiffness and the mesh load in gear system. The PISE method is based on evaluation of the geometric overlap of two assumedly rigid bodies and estimation of the contact force based on this artificial overlap area (or volume) and the singular stiffness (at the point
POSTER PRESENTATION Open Access Obesity has divergent effects on aortic stiffness
POSTER PRESENTATION Open Access Obesity has divergent effects on aortic stiffness in young and old velocity (PWV), a measure of central arterial stiffness, is an independent predictor of cardio- vascular on the association between obesity and aortic stiffness have been mixed, with some studies showing a positive
Nicholas M. Edwards; Stephen R. Daniels; Randall P. Claytor; Philip R. Khoury; Lawrence M. Dolan; Thomas R. Kimball; Elaine M. Urbina
Objective: Physical activity (PA) is associated with decreased levels of arterial stiffness in adults, but the relationship between PA and multiple measures of arterial stiffness in adolescents and young adults is not clear. The objective of this study was to test the hypothesis that PA is an independent predictor of multiple measures of arterial stiffness in adolescents and young adults.Materials\\/Methods:
Improving perceived hardness of haptic rendering via stiffness shifting: an initial study
Gabjong Han; Seokhee Jeon; Seungmoon Choi
2009-01-01
Rendering a stiff virtual surface using a force-feedback haptic in- terface has been one of the most classic and important research issues in haptics. In this paper, we present an initial study for a novel haptic rendering technique, named stiffness shifting, which greatly increases the perceived hardness of a virtual surface. The key idea of stiffness shifting is to use
STIFFNESS ANALYSIS OF MULTI-CHAIN PARALLEL ROBOTIC SYSTEMS WITH LOADING
Paris-Sud XI, Université de
1 STIFFNESS ANALYSIS OF MULTI-CHAIN PARALLEL ROBOTIC SYSTEMS WITH LOADING Anatol Pashkevich1 solution strategy of the kinetostatic equations, which allows computing the stiffness matrix for singular, stiffness analysis, kinetostatic modelling, loaded mode, Orthoglide robot Pashkevich A, Chablat D
Shih-feng Chen; Imin Kao
2002-01-01
In this paper, the conservative congruence transformation (CCT) for robot stiffness control is investigated by using geometrical methods. With the strategy of changing basis, it indicates that the formulation of stiffness matrix depends on the choice of coordinates. Thus, we show that the CCT can directly represent the spatial mapping relationship in robotic stiffness control. The CCT theory suggests a
Stiffness Synthesis of a Variable Geometry Six-Degrees-of-Freedom Double Planar Parallel Robot
Nabil Simaan; Moshe Shoham
2003-01-01
In this paper, we address the stiffness synthesis problem of vari- able geometry double planar parallel robots. For a desired stiffness matrix, the free geometrical variables are calculated as a solution of a corresponding polynomial system. Since in practice the set of free geometrical variables might be deficient, the suggested solution addresses also the case where not all stiffness matrix
Stiffness analysis for 6DOF mouth training parallel robot WY5
G. Carbone; H. Takanobu; M. Ceccarelli; A. Takanishi; K. Ohtsuki; M. Ohnishi; A. Okino
2003-01-01
In this paper a mouth opening and closing training robot, named WY-5 (Waseda Yamanashi version 5), is analyzed in terms of stiffness characteristics. The basic models and formulation are proposed in order to deduce the stiffness matrix as a function of the most important stiffness parameters of the WY-5 architecture. A numerical simulation is also presented to discuss main features
RANDALL KEITH ROBERTS
1984-01-01
This dissertation analyzes the effect of wrist force sensor mechanical stiffness on robot manipulator control. Typically, wrist force sensors for robotic systems have been designed and fabricated viewing the transducer as an isolated element, with mechanically stiff structures instrumented with strain gages being the most common configuration. Research has indicated, however, that force control system implementation with such stiff sensors
Konofagou, Elisa E.
Arterial stiffness identification of the human carotid artery using the stressstrain relationship in revised form 20 September 2011 Accepted 20 September 2011 Available online xxxx Keywords: Arterial stiffness Carotid artery Collagen Elastin Stressstrain relationship a b s t r a c t Arterial stiffness
Negative stiffness and negative Poisson's ratio in materials which undergo a phase transformation
Lakes, Roderic
of freedom beyond those ordinarily anticipated. We consider viscoelastic damping and negative stiffness or of viscoelastic damping. We consider several designed composite materials in which the negative stiffness arises, high viscoelastic damping and negative axial stiffness was observed [3 ] in lumped systems containing
Stable extremely-high-damping discrete viscoelastic systems due to negative stiffness elements
Lakes, Roderic
Stable extremely-high-damping discrete viscoelastic systems due to negative stiffness elements Yun with a viscoelastic damping element and a negative stiffness element can be made with overall viscoelastic damping; accepted 7 April 2004; published online 12 May 2004 Systems with negative stiffness constituents can have
Clipped viscous damping with negative stiffness for semi-active cable damping
F. Weber; C. Boston
2011-01-01
This paper investigates numerically and experimentally clipped viscous damping with negative stiffness for semi-active cable damping. From simulations it is concluded that unclipped and clipped viscous damping with negative stiffness is equivalent to unclipped and clipped LQR. It is shown that optimized unclipped viscous damping with negative stiffness generates critical cable damping by an anti-node at the actuator position. The
Compliant thin film patterns of stiff materials as platforms for stretchable electronics
Li, Teng
Compliant thin film patterns of stiff materials as platforms for stretchable electronics Teng Li. Such a wide serpentine, or other compliant patterns of stiff materials, can serve as a platform on which on a platform of a stiff material but a compliant pattern lying on an elastomeric substrate. These circuits
The SASS scattering coefficient algorithm
NASA Astrophysics Data System (ADS)
Bracalente, E. M.; Grantham, W. L.; Boggs, D. H.; Sweet, J. L.
1980-04-01
This paper describes the algorithms used to convert engineering unit data obtained from the Seasat-A satellite scatterometer (SASS) to radar scattering coefficients and associated supporting parameters. A description is given of the instrument receiver and related processing used by the scatterometer to measure signal power backscattered from the earth's surface. The applicable radar equation used for determining scattering coefficient is derived. Sample results of SASS data processed through current algorithm development facility (ADF) scattering coefficient algorithms are presented which include scattering coefficient values for both water and land surfaces. Scattering coefficient signatures for these two surface types are seen to have distinctly different characteristics. Scattering coefficient measurements of the Amazon rain forest indicate the usefulness of this type of data as a stable calibration reference target.
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
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…
Transformation of spherical harmonic coefficients to ellipsoidal harmonic coefficients
D. Dechambre; D. J. Scheeres
2002-01-01
Analytical expressions linking spherical harmonics gravity field expansions with ellipsoidal harmonics gravity field expansions are developed. Certain symmetries and simplifications for the transformation between the two are noted. Using the expressions, a numerical approach is developed and applied for the computation of ellipsoidal harmonic gravity coefficients using spherical harmonics coefficients as inputs. This method can be used to transform a
Carotid Stiffness and Physical Activity in Elderly—A Short Report of the SAPALDIA 3 Cohort Study
Caviezel, Seraina; Dratva, Julia; Schaffner, Emmanuel; Schindler, Christian; Endes, Simon; Autenrieth, Christine S.; Wanner, Miriam; Martin, Brian; de Groot, Eric; Gaspoz, Jean-Michel; Künzli, Nino; Probst-Hensch, Nicole; Schmidt-Trucksäss, Arno
2015-01-01
Introduction Regular physical activity has been shown to reduce cardiovascular disease risk in the general population. While smaller studies in specified groups (highly trained versus untrained individuals) indicate a certain dose-dependent effect of physical activity on the reduction of carotid stiffness (an indicator of subclinical vascular disease), it is unclear whether this association is present in a representative sample. Thus, we investigated this question cross-sectionally in participants from the population-based Swiss Cohort Study on Air Pollution And Lung and Heart Diseases In Adults (SAPALDIA). Methods Self-reported total, moderate and vigorous physical activity and distensibility as a measure of local arterial stiffness among 1636 participants aged 50 to 81 years without clinically manifest diseases were evaluated. Mixed regression models were used to examine associations of physical activity intensity with distensibility. Results Vigorous physical activity, but not total nor moderate physical activity, was significantly associated with increased distensibility (= reduced carotid stiffness) in univariate analyses (percent change in the geometric mean and 95% confidence interval per 1 standard deviation increment in vigorous physical activity = 2.54 (0.69; 4.43), p<0.01; in total physical activity = 1.62 (-0.22; 3.50), p = 0.08; in moderate physical activity = 0.70 (-1.12; 2.56), p = 0.45). These associations disappeared when we additionally adjusted for age. Conclusion After adjustment for the most important confounders and risk factors, we found no evidence for an association of physical activity with carotid stiffness in the general middle aged to elderly population. PMID:26035590
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.
Influence of Cohesive Energy and Chain Stiffness on Polymer Glass Formation
Wen-Sheng Xu; Karl F. Freed
2014-09-24
The generalized entropy theory is applied to assess the joint influence of the microscopic cohesive energy and chain stiffness on glass formation in polymer melts using a minimal model containing a single bending energy and a single (monomer averaged) nearest neighbor van der Waals energy. The analysis focuses on the combined impact of the microscopic cohesive energy and chain stiffness on the magnitudes of the isobaric fragility parameter $m_P$ and the glass transition temperature $T_g$. The computations imply that polymers with rigid structures and weak nearest neighbor interactions are the most fragile, while $T_g$ becomes larger when the chains are stiffer and/or nearest neighbor interactions are stronger. Two simple fitting formulas summarize the computations describing the dependence of $m_P$ and $T_g$ on the microscopic cohesive and bending energies. The consideration of the combined influence of the microscopic cohesive and bending energies leads to the identification of some important design concepts, such as iso-fragility and iso-$T_g$ lines, where, for instance, iso-fragility lines are contours with constant $m_P$ but variable $T_g$. Several thermodynamic properties are found to remain invariant along the iso-fragility lines, while no special characteristics are detected along the iso-$T_g$ lines. Our analysis supports the widely held view that fragility provides more fundamental insight for the description of glass formation than $T_g$.
Analysis of Brace Stiffness Influence on Stability of the Truss
NASA Astrophysics Data System (ADS)
Krajewski, M.; Iwicki, P.
2015-02-01
The paper is devoted to the numerical and experimental research of stability of a truss with side elastic supports at the top chord. The structure is a model of a real roof truss scaled by factor 1/4. The linear buckling analysis and non-linear static analysis were carried out. The buckling length factor for the compressed top chord was calculated and the limit load for the imperfect truss shell model with respect to brace stiffness was obtained. The relation between brace normal force and loading of the truss is presented. The threshold stiffness of braces necessary to obtain the maximum buckling load was found. The truss load bearing capacity obtained from numerical analysis was compared with Eurocode 3 requirements.
Depinning of stiff directed lines in random media.
Boltz, Horst-Holger; Kierfeld, Jan
2014-07-01
Driven elastic manifolds in random media exhibit a depinning transition to a state with nonvanishing velocity at a critical driving force. We study the depinning of stiff directed lines, which are governed by a bending rigidity rather than line tension. Their equation of motion is the (quenched) Herring-Mullins equation, which also describes surface growth governed by surface diffusion. Stiff directed lines are particularly interesting as there is a localization transition in the static problem at a finite temperature and the commonly exploited time ordering of states by means of Middleton's theorems [Phys. Rev. Lett. 68, 670 (1992)] is not applicable. We employ analytical arguments and numerical simulations to determine the critical exponents and compare our findings with previous works and functional renormalization group results, which we extend to the different line elasticity. We see evidence for two distinct correlation length exponents. PMID:25122245
Depinning of stiff directed lines in random media
NASA Astrophysics Data System (ADS)
Boltz, Horst-Holger; Kierfeld, Jan
2014-07-01
Driven elastic manifolds in random media exhibit a depinning transition to a state with nonvanishing velocity at a critical driving force. We study the depinning of stiff directed lines, which are governed by a bending rigidity rather than line tension. Their equation of motion is the (quenched) Herring-Mullins equation, which also describes surface growth governed by surface diffusion. Stiff directed lines are particularly interesting as there is a localization transition in the static problem at a finite temperature and the commonly exploited time ordering of states by means of Middleton's theorems [Phys. Rev. Lett. 68, 670 (1992), 10.1103/PhysRevLett.68.670] is not applicable. We employ analytical arguments and numerical simulations to determine the critical exponents and compare our findings with previous works and functional renormalization group results, which we extend to the different line elasticity. We see evidence for two distinct correlation length exponents.
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
Stiff filamentous virus translocations through solid-state nanopores
NASA Astrophysics Data System (ADS)
McMullen, Angus; de Haan, Hendrick W.; Tang, Jay X.; Stein, Derek
2014-06-01
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.
Mechanism of regulation of stem cell differentiation by matrix stiffness.
Lv, Hongwei; Li, Lisha; Sun, Meiyu; Zhang, Yin; Chen, Li; Rong, Yue; Li, Yulin
2015-01-01
Stem cell behaviors are regulated by multiple microenvironmental cues. As an external signal, mechanical stiffness of the extracellular matrix is capable of governing stem cell fate determination, but how this biophysical cue is translated into intracellular signaling remains elusive. Here, we elucidate mechanisms by which stem cells respond to microenvironmental stiffness through the dynamics of the cytoskeletal network, leading to changes in gene expression via biophysical transduction signaling pathways in two-dimensional culture. Furthermore, a putative rapid shift from original mechanosensing to de novo cell-derived matrix sensing in more physiologically relevant three-dimensional culture is pointed out. A comprehensive understanding of stem cell responses to this stimulus is essential for designing biomaterials that mimic the physiological environment and advancing stem cell-based clinical applications for tissue engineering. PMID:26012510
Association between arterial stiffness and peritoneal small solute transport rate.
Zhe, Xing-wei; Tian, Xin-kui; Chen, Wei; Guo, Li-juan; Gu, Yue; Chen, Hui-min; Tang, Li-jun; Wang, Tao
2008-05-01
While cardiovascular disease accounts for 40-50% of the mortality in dialysis patients, and while a high peritoneal transport in continuous ambulatory peritoneal dialysis (CAPD) is an independent predictor of outcome, it is unclear if there are any links. Aortic stiffness has become established as a cardiovascular risk factor. We thus studied pulse wave velocity (PWV) in CAPD patients to explore the possible link between peritoneal small solute transport and aortic stiffness. CAPD patients (n = 76, 27 M/49 F) in our center were included in the present study. Aortic stiffness was assessed by brachial pulse pressure (PP) and carotid-femoral PWV. Patients' peritoneal small solute transport rate was assessed by D/P(cr) at 4 h. Extracellular water over total body water (E/T ratio) was assessed by means of bioimpedance analysis. C-reactive protein was also measured. Carotid-femoral PWV was positively associated with patients' age (r = 0.555; P < 0.01), time on peritoneal dialysis (r = 0.332; P < 0.01), diabetic status (r = 0.319; P < 0.01), D/P(cr) (r = 0.241; P < 0.05), PP (r = 0.475; P < 0.01), and E/T (r = 0.606; P < 0.01). In a multivariate regression analysis, carotid-femoral PWV was independently determined by E/T (P < 0.01), PP (P < 0.01), age (P < 0.01), and D/P(cr) (P < 0.05). D/P(cr), in addition to E/T, age, and PP, was an independent predictor of elevated carotid-femoral PWV in CAPD patients, suggesting that there might be a link between high aortic stiffness and increased peritoneal small solute transport rate. PMID:18471172
On a high-potential variable flexural stiffness device
NASA Astrophysics Data System (ADS)
Henke, Markus; Gerlach, Gerald
2013-05-01
There are great efforts in developing effective composite structures for lightweight constructions for nearly every field of engineering. This concerns for example aeronautics and spacecrafts, but also automotive industry and energy harvesting applications. Modern concepts of lightweight components try to make use of structures with properties which can be adjusted in a controllable was. However, classic composite materials can only slightly adapt to varying environmental conditions because most materials, like carbon or glass-fiber composites show properties which are time-constant and not changeable. This contribution describes the development, the potential and the limitations of novel smart, self-controlling structures which can change their mechanical properties - e.g. their flexural stiffness - by more then one order of magnitude. These structures use a multi-layer approach with a 10-layer stack of 0.75 mm thick polycarbonate. The set-up is analytically described and its mechanical behavior is predicted by finite element analysis done with ABAQUS. The layers are braided together by an array of shape memory alloy (SMA) wires, which can be activated independently. Depending on the temperature applied by the electrical current flowing through the wires and the corresponding contraction the wires can tightly clamp the layers so that they cannot slide against each other due to friction forces. In this case the multilayer acts as rigid beam with high stiffness. If the friction-induced shear stress is smaller than a certain threshold, then the layers can slide over each other and the multilayer becomes compliant under bending load. The friction forces between the layers and, hence, the stiffness of the beam is controlled by the electrical current through the wires. The more separate parts of SMA wires the structure has the larger is the number of steps of stiffness changes of the flexural beam.
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.
A geometric approach to the algorithmic tangent stiffness
G. Romano; M. Diaco; R. Barretta
The elastoplastic tangent stiffness is the linear operator which provides the stress rate corresponding to a prescribed strain\\u000a rate. As such, it plays a central role in the computational aspects of elastoplastic problems. According to the usual approach\\u000a to the nonlinear evolutive analysis of elastoplastic models, a finite time-step is considered and the evolution law describing\\u000a the constitutive behavior is
Influence of substrate stiffness on circulating progenitor cell fate.
Fioretta, Emanuela S; Fledderus, Joost O; Baaijens, Frank P T; Bouten, Carlijn V C
2012-03-15
In situ vascular tissue engineering (TE) aims at regenerating vessels using implanted synthetic scaffolds. An envisioned strategy is to capture and differentiate progenitor cells from the bloodstream into the porous scaffold to initiate tissue formation. Among these cells are the endothelial colonies forming cells (ECFCs) that can differentiate into endothelial cells and transdifferentiate into smooth muscle cells under biochemical stimulation. The influence of mechanical stimulation is unknown, but relevant for in situ vascular TE because the cells perceive a change in mechanical environment when captured inside the scaffold, where they are shielded from blood flow induced shear stresses. Here we investigate the effects of substrate stiffness as one of the environmental mechanical cues to control ECFC fate within scaffolds. ECFCs were seeded on soft (3.58±0.90 kPa), intermediate (21.59±2.91 kPa), and stiff (93.75±18.36 kPa) fibronectin-coated polyacrylamide gels, as well as on glass controls, and compared to peripheral blood mononuclear cells (PBMC). Cell behavior was analyzed in terms of adhesion (vinculin staining), proliferation (BrdU), phenotype (CD31, ?SMA staining, and flow cytometry), and collagen production (col I, III, and IV). While ECFCs adhesion and proliferation increased with substrate stiffness, no change in phenotype was observed. The cells produced no collagen type I, but abundant amounts of collagen type III and IV, albeit in a stiffness-dependent organization. PBMCs did not adhere to the gels, but they did adhere to glass, where they expressed CD31 and collagen type III. Addition mechanical cues, such as cyclic strains, should be studied to further investigate the effect of the mechanical environment on captured circulating cells for in situ TE purposes. PMID:22169135
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.
Nanoscale structure and microscale stiffness of DNA nanotubes.
Schiffels, Daniel; Liedl, Tim; Fygenson, Deborah K
2013-08-27
We measure the stiffness of tiled DNA nanotubes (HX-tubes) as a function of their (defined) circumference by analyzing their micrometer-scale thermal deformations using fluorescence microscopy. We derive a model that relates nanoscale features of HX-tube architecture to the measured persistence lengths. Given the known stiffness of double-stranded DNA, we use this model to constrain the average spacing between and effective stiffness of individual DNA duplexes in the tube. A key structural feature of tiled nanotubes that can affect stiffness is their potential to form with discrete amounts of twist of the DNA duplexes about the tube axis (supertwist). We visualize the supertwist of HX-tubes using electron microscopy of gold nanoparticles, attached to specific sites along the nanotube. This method reveals that HX-tubes tend not to form with supertwist unless forced by sequence design, and, even when forced, supertwist is reduced by elastic deformations of the underlying DNA lattice. We compare the hybridization energy gained upon closing a duplex sheet into a tube with the elastic energy paid for deforming the sheet to allow closure. In estimating the elastic energy we account for bending and twisting of the individual duplexes as well as shearing between them. We find the minimum supertwist state has minimum free energy, and global untwisting of forced supertwist is energetically favorable, consistent with our experimental data. Finally, we show that attachment of Cy3 dyes or changing counterions can cause nanotubes to adopt a permanent writhe with micrometer-scale pitch and amplitude. We propose that the coupling of local twist and global counter-twist may be useful in characterizing perturbations of DNA structure. PMID:23879368
Stiffness Measurement of Burkitt's Lymphoma Cells with Atomic Force Microscopy
Mi Li; Lianqing Liu; Ning Xi; Yuechao Wang; Zaili Dong; Xiubin Xiao; Weijing Zhang
2010-01-01
Cell stiffness is closely related to human health and diseases. Measuring the mechanical property of individual cells may help us to understand the mechanism of diseases at cell level and provide new methods for disease diagnosis and personalized treatment. In this paper, the poly-l-lysine was used to immobilize Burkitt's lymphoma (BL)cells onto the glass substrate for being imaged in fluid
Experimental exposure to diesel exhaust increases arterial stiffness in man
Magnus Lundbäck; Nicholas L Mills; Andrew Lucking; Stefan Barath; Ken Donaldson; David E Newby; Thomas Sandström; Anders Blomberg
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
Suppression of large-scale perturbations by stiff solid
Vladimír Balek; Matej Škovran
2015-01-28
Evolution of large-scale scalar perturbations in the presence of stiff solid (solid with pressure to energy density ratio > 1/3) is studied. If the solid dominated the dynamics of the universe long enough, the perturbations could end up suppressed by as much as several orders of magnitude. To avoid too steep large-angle power spectrum of CMB, radiation must have prevailed over the solid long enough before recombination.
STIFF-INPLANE TILTROTOR AEROMECHANICS INVESTIGATION USING TWO MULTIBODY ANALYSES
Jinwei Shen; Pierangelo Masarati; Beatrice Roget; David J. Piatak; Mark W. Nixon; Jeffrey D. Singleton
This paper presents the development of two multibody dynami cs models to predict the whirl-flutter stability of a stiff-inplane tiltrotor wind-tunnel model and correlates the predic- tions with experimental data. Comprehensive, multibody-b ased dynamics analyses of rotorcraft enable modeling and simulation of the rotor system at a high l evel of detail so that complex mechanics and nonlinear effects associated
Nonlinear Effects in Stiffness Modeling of Robotic Manipulators
Anatoly Pashkevich; Alexandr Klimchik; Damien Chablat
2009-01-01
The paper focuses on the enhanced stiffness modeling of robotic manipulators\\u000aby taking into account influence of the external force\\/torque acting upon the\\u000aend point. It implements the virtual joint technique that describes the\\u000acompliance of manipulator elements by a set of localized six-dimensional\\u000asprings separated by rigid links and perfect joints. In contrast to the\\u000aconventional formulation, which is
Arterial stiffness, central hemodynamics, and cardiovascular risk in hypertension
Palatini, Paolo; Casiglia, Edoardo; G?sowski, Jerzy; G?uszek, Jerzy; Jankowski, Piotr; Narkiewicz, Krzysztof; Saladini, Francesca; Stolarz-Skrzypek, Katarzyna; Tikhonoff, Valérie; Van Bortel, Luc; Wojciechowska, Wiktoria; Kawecka-Jaszcz, Kalina
2011-01-01
This review summarizes several scientific contributions at the recent Satellite Symposium of the European Society of Hypertension, held in Milan, Italy. Arterial stiffening and its hemodynamic consequences can be easily and reliably measured using a range of noninvasive techniques. However, like blood pressure (BP) measurements, arterial stiffness should be measured carefully under standardized patient conditions. Carotid-femoral pulse wave velocity has been proposed as the gold standard for arterial stiffness measurement and is a well recognized predictor of adverse cardiovascular outcome. Systolic BP and pulse pressure in the ascending aorta may be lower than pressures measured in the upper limb, especially in young individuals. A number of studies suggest closer correlation of end-organ damage with central BP than with peripheral BP, and central BP may provide additional prognostic information regarding cardiovascular risk. Moreover, BP-lowering drugs can have differential effects on central aortic pressures and hemodynamics compared with brachial BP. This may explain the greater beneficial effect provided by newer antihypertensive drugs beyond peripheral BP reduction. Although many methodological problems still hinder the wide clinical application of parameters of arterial stiffness, these will likely contribute to cardiovascular assessment and management in future clinical practice. Each of the abovementioned parameters reflects a different characteristic of the atherosclerotic process, involving functional and/or morphological changes in the vessel wall. Therefore, acquiring simultaneous measurements of different parameters of vascular function and structure could theoretically enhance the power to improve risk stratification. Continuous technological effort is necessary to refine our methods of investigation in order to detect early arterial abnormalities. Arterial stiffness and its consequences represent the great challenge of the twenty-first century for affluent countries, and “de-stiffening” will be the goal of the next decades. PMID:22174583
Stiffness detection and reduction in discrete stochastic simulation of biochemical systems
Pu, Yang; Watson, Layne T.; Cao, Yang
2011-01-01
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. PMID:21303090
Temporal response of arterial stiffness to ultra-marathon.
Burr, J F; Phillips, A A; Drury, T C; Ivey, A C; Warburton, D E R
2014-07-01
The purpose of this investigation was to characterize the arterial stiffness of male ultra-marathon runners (n = 9) using pulse wave velocity (cfPWV) and radial tonometry over the course of an ultra-marathon and during recovery. Measures were collected at rest, immediately following 45?km/75?km of running, then following 60 and 90?min of recovery. No statistical difference was found between baseline cfPWV and normative values. The cfPWV of ultra-endurance runners decreased at 45?km (3.4 ± 1.6?m/s, p=0.006), followed by an increase (1.6 ± 1.8?m/s, p = 0.04) toward baseline levels at the 75?km mark. Radial tonometry measures also indicated small artery stiffness was transiently increased after 75?km. The amount of training time (r = 0.82, p = 0.007) and the duration of a typical training session (r = 0.73, p = 0.03) were correlated strongly with persisting decrements in large artery compliance at 60?min of recovery. The finding that arterial stiffness decreased at the 45?km distance and then reverted back toward baseline levels with prolonged running, may indicate a role of exercise duration or accumulated stress for affecting vascular compliance. At present, it is premature to suggest that athletes should alter training or racing practices to protect vascular health. PMID:24408767
Integral tau methods for stiff stochastic chemical systems
NASA Astrophysics Data System (ADS)
Yang, Yushu; Rathinam, Muruhan; Shen, Jinglai
2011-01-01
Tau leaping methods enable efficient simulation of discrete stochastic chemical systems. Stiff stochastic systems are particularly challenging since implicit methods, which are good for stiffness, result in noninteger states. The occurrence of negative states is also a common problem in tau leaping. In this paper, we introduce the implicit Minkowski-Weyl tau (IMW-?) methods. Two updating schemes of the IMW-? methods are presented: implicit Minkowski-Weyl sequential (IMW-S) and implicit Minkowski-Weyl parallel (IMW-P). The main desirable feature of these methods is that they are designed for stiff stochastic systems with molecular copy numbers ranging from small to large and that they produce integer states without rounding. This is accomplished by the use of a split step where the first part is implicit and computes the mean update while the second part is explicit and generates a random update with the mean computed in the first part. We illustrate the IMW-S and IMW-P methods by some numerical examples, and compare them with existing tau methods. For most cases, the IMW-S and IMW-P methods perform favorably.
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
Glycine Receptor Autoimmune Spectrum With Stiff-Man Syndrome Phenotype
McKeon, Andrew; Martinez-Hernandez, Eugenia; Lancaster, Eric; Matsumoto, Joseph Y.; Harvey, Robert J.; McEvoy, Kathleen M.; Pittock, Sean J.; Lennon, Vanda A.; Dalmau, Josep
2013-01-01
Objectives To determine whether glycine receptor ?1 subunit-specific autoantibodies (GlyR?1-IgG) occur in a broader spectrum of brainstem and spinal hyperexcitability disorders than the progressive encephalomyelitis with rigidity and myoclonus phenotype recognized to date, and to ascertain disease specificity. Design Retrospective, case-control study. Settings Mayo Clinic, Rochester, Minnesota, and University of Barcelona, Spain. Patients Eighty-one patients with stiff-man syndrome phenotype, 80 neurologic control subjects, and 20 healthy control subjects. Intervention Glycine receptor ?1–transfected cells to test serum or cerebrospinal fluid from cases and control subjects. Main Outcome Measures Frequency of GlyR?1-IgG positivity among stiff-man syndrome phenotype cases and control subjects. Comparison of GlyR?1-IgG seropositive and seronegative cases. Results Seropositive cases (12% of cases) included 9 with stiff-man syndrome (4 classic; 5 variant; 66% were glutamic acid decarboxylase 65–IgG positive) and 1 with progressive encephalomyelitis with rigidity and myoclonus. Immunotherapy responses were noted more frequently in GlyR?1-IgG–positive cases (6 of 7 improved) than in seronegative cases (7 of 25 improved; P=.02). The single seropositive control patient had steroid-responsive vision loss and optic atrophy with inflammatory cerebrospinal fluid. Conclusions Glycine receptor ?1–IgG aids identification of autoimmune brainstem/spinal cord hyperexcitability disorders and may extend to the glycinergic visual system. PMID:23090334
Role of Inflammation and Substrate Stiffness in Cancer Cell Transmigration
NASA Astrophysics Data System (ADS)
Hamilla, Susan; Stroka, Kimberly; Aranda-Espinoza, Helim
2013-03-01
Cancer metastasis, the ability for cancer cells to break away from the primary tumor site and spread to other organs of the body, is one of the main contributing factors to the deadliness of the disease. One of the rate-limiting steps in cancer metastasis that is not well understood is the adhesion of tumor cells to the endothelium followed by transmigration. Other factors include substrate stiffness and inflammation. To test these parameters, we designed an in vitro model of transendothelial migration. Our results suggest that cancer cell transmigration is a two-step process in which they first incorporate into the endothelium before migrating through. It was observed that the cumulative fraction of cancer cells that incorporate into the endothelium increases over time. Unlike leukocytes, which can directly transmigrate through the endothelium, cancer cells appear to have a two-step process of transmigration. Our results indicate that inflammation does not act as a signal for cancer cells to localize at specific sites and transmigrate similarly to leukocytes. Cancer cell transmigration also does not vary with substrate stiffness indicating that tissue stiffness may not play a role in cancer's propensity to metastasize to certain tissues.
Forced vibration of flexible body systems. A dynamic stiffness method
NASA Astrophysics Data System (ADS)
Liu, T. S.; Lin, J. C.
1993-10-01
Due to the development of high speed machinery, robots, and aerospace structures, the research of flexible body systems undergoing both gross motion and elastic deformation has seen increasing importance. The finite element method and modal analysis are often used in formulating equations of motion for dynamic analysis of the systems which entail time domain, forced vibration analysis. This study develops a new method based on dynamic stiffness to investigate forced vibration of flexible body systems. In contrast to the conventional finite element method, shape functions and stiffness matrices used in this study are derived from equations of motion for continuum beams. Hence, the resulting shape functions are named as dynamic shape functions. By applying the dynamic shape functions, the mass and stiffness matrices of a beam element are derived. The virtual work principle is employed to formulate equations of motion. Not only the coupling of gross motion and elastic deformation, but also the stiffening effect of axial forces is taken into account. Simulation results of a cantilever beam, a rotating beam, and a slider crank mechanism are compared with the literature to verify the proposed method.
Recursive Construction of Operator Product Expansion Coefficients
NASA Astrophysics Data System (ADS)
Holland, Jan; Hollands, Stefan
2015-06-01
We derive a novel formula for the derivative of operator product expansion (OPE) coefficients with respect to a coupling constant. The formula involves just the OPE coefficients themselves but no further input, and is in this sense self-consistent. Furthermore, unlike other formal identities of this general nature in quantum field theory (such as the formal expression for the Lagrangian perturbation of a correlation function), our formula requires no further UV-renormalization, i.e., it is completely well-defined from the start. This feature is a result of a cancelation of UV- and IR-divergences between various terms in our identity. Our proof, and an analysis of the features of the identity, is given for the example of massive, Euclidean theory in 4 dimensional Euclidean space. It relies on the renormalization group flow equation method and is valid to arbitrary, but finite orders in perturbation theory. The final formula, however, makes neither explicit reference to the renormalization group flow, nor to perturbation theory, and we conjecture that it also holds non-perturbatively. Our identity can be applied constructively because it gives a novel recursive algorithm for the computation of OPE coefficients to arbitrary (finite) perturbation order in terms of the zeroth order coefficients corresponding to the underlying free field theory, which in turn are trivial to obtain. We briefly illustrate the relation of this method to more standard methods for computing the OPE in some simple examples.
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.
Prediction in random coefficient regression
Rudolf Beran
1995-01-01
Random coefficient regression and autoregressive models are important in diverse applications such as the classical statistical analysis of random and mixed effects models, the modelling of certain econometric and biological time series, and as a means for image compression. This paper develops nonparametric prediction intervals for a random coefficient regression model. The construction of these intervals requires a consistent estimate
The Percentage Bend Correlation Coefficient.
ERIC Educational Resources Information Center
Wilcox, Rand R.
1994-01-01
The percentage bend correlation coefficient is introduced as one way to address the problem that the usual correlation coefficient is highly nonrobust. While this method is not a replacement for the usual test, it can offer advantages in terms of power and Type I errors. (SLD)
NASA Astrophysics Data System (ADS)
Chaudhuri, Ovijit; Koshy, Sandeep T.; Branco da Cunha, Cristiana; Shin, Jae-Won; Verbeke, Catia S.; Allison, Kimberly H.; Mooney, David J.
2014-10-01
In vitro models of normal mammary epithelium have correlated increased extracellular matrix (ECM) stiffness with malignant phenotypes. However, the role of increased stiffness in this transformation remains unclear because of difficulties in controlling ECM stiffness, composition and architecture independently. Here we demonstrate that interpenetrating networks of reconstituted basement membrane matrix and alginate can be used to modulate ECM stiffness independently of composition and architecture. We find that, in normal mammary epithelial cells, increasing ECM stiffness alone induces malignant phenotypes but that the effect is completely abrogated when accompanied by an increase in basement-membrane ligands. We also find that the combination of stiffness and composition is sensed through ?4 integrin, Rac1, and the PI3K pathway, and suggest a mechanism in which an increase in ECM stiffness, without an increase in basement membrane ligands, prevents normal ?6?4 integrin clustering into hemidesmosomes.
Specific Storage as a Poroelastic Coefficient
NASA Astrophysics Data System (ADS)
Green, D. H.; Wang, H. F.
1990-07-01
A definition for the specific storage coefficient Ss is given which is unambiguous for general isotropic three-dimensional aquifer elasticity. In every representative elementary volume, Ss is the fluid volume released from storage per unit decline in hydraulic head, per unit bulk volume, under conditions such that there is no strain in two orthogonal directions, and the total normal stress in the third orthogonal direction is constant. The specific storage coefficient is a point property of the aquifer and is defined independently of problem domain stress and head boundary conditions. The expression for Ss in terms of aquifer and fluid compressibilities is identical to the familiar forms obtained assuming zero horizontal strain and constant overburden in an aquifer, although it is not restricted to these conditions. As a point property of the fluid-saturated material, the specific storage coefficient is one of four constants in the general constitutive poroelastic equations relating three-dimensional aquifer stress and strain to fluid pressure and dilatation. Written in terms of Ss, these equations show that pore fluid mass diffusion is governed by a diffusivity equal to the ratio of hydraulic conductivity to specific storage under arbitrary boundary conditions. It is shown that Ss controls slow compressional body wave velocity in the low frequency limit and that the uniaxial aquifer compressibility ? is not necessarily related to the vertical direction.
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.
Munakata, Masanori
2014-01-01
Arterial stiffness is a vascular measure that has been reported to predict cardiovascular events. It is important to measure arterial stiffness in order to determine current vascular status and treatment strategy. Brachial-ankle pulse wave velocity (baPWV) is a unique measure of systemic arterial stiffness that is measured by brachial and tibial arterial wave analyses. Measurement of baPWV is easy and is reproducible. For more than a decade, this measure has been used broadly in East Asian countries. Meta-analysis of cohort studies conducted in the general population with hypertension, diabetes, or end-stage renal disease, and other high-risk individuals have shown that a 1 m/s increase in baPWV is associated with 12% increase in the risk of cardiovascular events. Thus, the Japanese Circulation Society has proposed that a baPWV of 1800 cm/s is a threshold for high-risk category. For baPWV to be clinically applicable, we must confirm that circulation of the lower limbs are normal by examining brachial ankle blood pressure index. In cases of peripheral arterial disease, the reliability of baPWV measurement is attenuated. To further confirm the clinical usefulness of this measure, we need to examine the hypothesis that baPWV-guided therapy could improve prognosis in high-risk patients. PMID:25392144
Solute concentration effect on osmotic reflection coefficient.
Adamski, R P; Anderson, J L
1983-01-01
A theory for the effect of concentration on osmotic reflection coefficient, correct to first order, was developed at the molecular level by considering the effect of solute-solute interactions on solute concentration and the fluid stress tensor within a solvent-filled pore. The solvent was modeled as a continuous fluid and potential energies between solute molecules and the pore wall were assumed to be pairwise additive. Although the theory is more general, calculations are presented only for excluded volume effects (hard-sphere for solute, hard-wall for pore). The relationship between the first-order concentration effect and the infinite dilution value of reflection coefficient appears to be geometry independent. The theory is discussed in light of experimental studies of osmotic flow that have recently appeared in the literature. PMID:6626681
Benjamin G. Serpell; Nick B. Ball; Jennie M. Scarvell; Paul N. Smith
2012-01-01
The ‘stiffness’ concept originates from Hooke's law which states that the force required to deform an object is related to a spring constant and the distance that object is deformed. Research into stiffness in the human body is undergoing unprecedented popularity; possibly because stiffness has been associated with sporting performance and some lower limb injuries. However, some inconsistencies surrounding stiffness
The torsional stiffness of thin duralumin shells subjected to large torques
NASA Technical Reports Server (NTRS)
Kuhn, Paul
1934-01-01
This report gives a simple method of estimating the torsional stiffness of thin shells, such as box beams or stressed-skin wings under large torque loads. A general efficiency chart for shells in torsion is established, based on the assumption that the efficiency of the web sheet in resisting deformation decreases linearly with the average stress. The chart is used to calculate the torsional deflections of eight box beams, a test wing panel, and a complete wing; the results of the calculations are shown in comparison with the test results. The agreement is probably as good as might be expected considering the empirical nature of the method and the well-known dispersion between results of tests on thin sheet-metal structures.
Negative coefficient of normal restitution.
Müller, Patric; Krengel, Dominik; Pöschel, Thorsten
2012-04-01
This paper shows that negative coefficients of normal restitution occur inevitably when the interaction force between colliding particles is finite. We derive an explicit criterion showing that for any set of material properties there is always a collision geometry leading to negative restitution coefficients. While from a phenomenological point of view, negative coefficients of normal restitution appear rather artificial, this phenomenon is generic and implies an important overlooked limitation of the widely used hard sphere model. The criterion is explicitly applied to two paradigmatic situations: for the linear dashpot model and for viscoelastic particles. In addition, we show that for frictional particles the phenomenon is less pronounced than for smooth spheres. PMID:22680468
Negative coefficient of normal restitution
NASA Astrophysics Data System (ADS)
Müller, Patric; Krengel, Dominik; Pöschel, Thorsten
2012-04-01
This paper shows that negative coefficients of normal restitution occur inevitably when the interaction force between colliding particles is finite. We derive an explicit criterion showing that for any set of material properties there is always a collision geometry leading to negative restitution coefficients. While from a phenomenological point of view, negative coefficients of normal restitution appear rather artificial, this phenomenon is generic and implies an important overlooked limitation of the widely used hard sphere model. The criterion is explicitly applied to two paradigmatic situations: for the linear dashpot model and for viscoelastic particles. In addition, we show that for frictional particles the phenomenon is less pronounced than for smooth spheres.
Multi-fingered haptic palpation utilizing granular jamming stiffness feedback actuators
NASA Astrophysics Data System (ADS)
Li, Min; Ranzani, Tommaso; Sareh, Sina; Seneviratne, Lakmal D.; Dasgupta, Prokar; Wurdemann, Helge A.; Althoefer, Kaspar
2014-09-01
This paper describes a multi-fingered haptic palpation method using stiffness feedback actuators for simulating tissue palpation procedures in traditional and in robot-assisted minimally invasive surgery. Soft tissue stiffness is simulated by changing the stiffness property of the actuator during palpation. For the first time, granular jamming and pneumatic air actuation are combined to realize stiffness modulation. The stiffness feedback actuator is validated by stiffness measurements in indentation tests and through stiffness discrimination based on a user study. According to the indentation test results, the introduction of a pneumatic chamber to granular jamming can amplify the stiffness variation range and reduce hysteresis of the actuator. The advantage of multi-fingered palpation using the proposed actuators is proven by the comparison of the results of the stiffness discrimination performance using two-fingered (sensitivity: 82.2%, specificity: 88.9%, positive predicative value: 80.0%, accuracy: 85.4%, time: 4.84 s) and single-fingered (sensitivity: 76.4%, specificity: 85.7%, positive predicative value: 75.3%, accuracy: 81.8%, time: 7.48 s) stiffness feedback.
Li, Yanlei; Hanssen, Henner; Cordes, Mareike; Rossmeissl, Anja; Endes, Simon; Schmidt-Trucksäss, Arno
2015-08-01
Exercise training has different effects on arterial stiffness according to training modalities. The optimal exercise modality for improvement of arterial function in normotensive and hypertensive individuals has not been well established. In this review, we aim to evaluate the effects of aerobic, resistance and combined aerobic and resistance training on arterial stiffness in individuals with and without hypertension. We systematically searched the Pubmed and Web of Science database from 1985 until December 2013 for relevant randomised controlled trials (RCTs). The data were extracted by one investigator and checked by a second investigator. The training effects on arterial stiffness were estimated using weighted mean differences of the relative changes (%) with 95% confidence intervals (CIs). We finally reviewed the results from 17 RCTs. The available evidence indicates that aerobic exercise tends to have a beneficial effect on arterial stiffness in normotensive and hypertensive patients, but does not affect arterial stiffness in patients with isolated systolic hypertension. Resistance exercise has differing effects on arterial stiffness depending on type and intensity. Vigorous resistance training is associated with an increase in arterial stiffness. There seem to be no unfavourable effects on arterial stiffness if the training is of low intensity, in a slow eccentric manner or with lower limb in healthy individuals. Combined training has neutral or even a beneficial effect on arterial stiffness. In conclusion, our review shows that exercise training has varying effects on arterial stiffness depending on the exercise modalities. PMID:25251989
An incrementally non-linear model for clays with directional stiffness and a small strain emphasis
NASA Astrophysics Data System (ADS)
Tu, Xuxin
In response to construction activities and loads from permanent structures, soil generally is subjected to a variety of loading modes varying both in time and location. It also has been increasingly appreciated that the strains around well-designed foundations, excavations and tunnels are mostly small, with soil responses at this strain level generally being non-linear and anisotropic. To make accurate prediction of the performance of a geo-system, it is highly desirable to understand soil behavior at small strains along multiple loading directions, and accordingly to incorporate these responses in an appropriate constitutive model implemented in a finite element analysis. This dissertation presents a model based on a series of stress probe tests with small strain measurements performed on compressible Chicago glacial clays. The proposed model is formulated in an original constitutive framework, in which the tangent stiffness matrix is constructed in accordance with the mechanical nature of frictional materials and the tangent moduli therein are described explicitly. The stiffness description includes evolution relations with regard to length of stress path, and directionality relations in terms of stress path direction. The former relations provide distinctive definitions for small-strain and large-strain behaviors, and distinguish soil responses in shearing and compression. The latter relations make this model incrementally non-linear and thus capable of modeling inelastic behavior. A new algorithm based on a classical substepping scheme is developed to numerically integrate this model. A consistent tangent matrix is derived for the proposed model with the upgraded substepping scheme. The code is written in FORTRAN and implemented in FEM via UMAT of ABAQUS. The model is exercised in a variety of applications ranging from oedometer, triaxial and biaxial test simulations to a C-class prediction for a well-instrumented excavation. The computed results indicate that this model is successful in reproducing soil responses in both laboratory and field situations.
Mechanically Induced Reactive Gliosis Causes ATP-Mediated Alterations in Astrocyte Stiffness
Miller, William J.; Leventhal, Ilya; Scarsella, David; Haydon, Philip G.; Janmey, Paul
2009-01-01
Abstract Reactive gliosis is a process triggered in astrocytes after traumatic injury, yet the exact consequences of gliosis on cellular survival and neural regenerative processes in the injured brain remain only partly understood. One recently discovered feature influencing neuronal growth and differentiation is the physical stiffness of the environment surrounding pioneering neurites. In this study, the mechanical properties of cultured cortical astrocytes are measured following a mechanical stretch injury that induces reactive gliosis. In mechanically injured cultures, there was a significant increase in glial fibrillary acidic protein (GFAP) immunoreactivity 24?h following a rapid, transient 15% strain. In these same cultures, astrocytes in the surrounding region—the “mechanical penumbra”—also exhibited increased GFAP immunoreactivity compared to naive cultures. Correlated with these changes in GFAP was a general softening of the non-nuclear regions of the astrocytes, both in the injured and penumbra cells, as measured by atomic force microscopy (AFM). The elastic modulus in naive cultures was observed to be 57.7?±?5.8?kPa in non-nuclear regions of naive cultures, while 24?h after injury the modulus was observed to be 26.4?±?4.9?kPa in the same region of injured cells. In the penumbra of injured cultures, the modulus was 23.7?±?3.6?kPa. Alterations in astrocyte stiffness in the area of injury and mechanical penumbra were ameliorated by pretreating cultures with a nonselective P2 receptor antagonist (PPADS). Since neuronal cells generally prefer softer substrates for growth and neurite extension, these findings may indicate that the mechanical characteristics of reactive astrocytes are favorable for neuronal recovery after traumatic brain injury. PMID:19331521
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.
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.
The Seebeck coefficient of iodine
Perez-Fernandez, Domingo Miguel
1968-01-01
THE SEEBECK COEFFICIENT OF IODINE A Thesis By DOMINGO M. PEREZ-F~EZ Submitted to the Graduate College of the Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE January 1968 Major Subject...; Physics THE SEEBECK COEFFICIENT OF IODINE A Thesis By DOMINGO M. PEREZ-FERNANDEZ Approved as to style and content by: ( airman of Co ittee) (Member) (Head of Depa ment) (Member) ( ember) (Member) (Member) January 1968 ACKNONLEDGEMENTS...
T. J. S. Abrahamsson; J. H. Saellstroem
1996-01-01
Linear vibrations are studied for a straight uniform finite beam element of general orientation spinning at a constant angular speed about a fixed axis in the inertial space. The gyroscopic and circulatory matrices and also the geometric stiffness matrix of the beam element are presented. The effect of the centrifugal static axial load on the bending and torsional dynamic stiffnesses
Stochastic Plane Stress Analysis with Elementary Stiffness Matrix Decomposition Method
NASA Astrophysics Data System (ADS)
Er, G. K.; Wang, M. C.; Iu, V. P.; Kou, K. P.
2010-05-01
In this study, the efficient analytical method named elementary stiffness matrix decomposition (ESMD) method is further investigated and utilized for the moment evaluation of stochastic plane stress problems in comparison with the conventional perturbation method in stochastic finite element analysis. In order to evaluate the performance of this method, computer programs are written and some numerical results about stochastic plane stress problems are obtained. The numerical analysis shows that the computational efficiency is much increased and the computer EMS memory requirement can be much reduced by using ESMD method.
A. I. Aptekarev; A. Branquinho
1997-01-01
Transformations of the measure of orthogonality for orthogonal polynomials, namely Freud transformations, are considered. Jacobi matrix of the recurrence coefficients of orthogonal polynomials possesses an isospectral deformation under these transformations. Dynamics of the coefficients are described by generalized Toda equations. The classical Toda lattice equations are the simplest special case of dynamics of the coefficients under the Freud transformation of
An index theorem for band-dominated oper-ators with slowly oscillating coefficients (af-
Willett, Rufus
An index theorem for band-dominated oper- ators with slowly oscillating coefficients (af- ter In this piece we prove an index theorem for band-dominated operators (BDOs) with slowly oscillating coefficients an index theorem for general BDOs (i.e. with coefficients that are not necessarily slowly oscillating) on l
PURE WATER ABSORPTION COEFFICIENT AROUND 400NM: LAB MEASURED VERSUS FIELD OBSERVED
Lee, Zhongping
PURE WATER ABSORPTION COEFFICIENT AROUND 400NM: LAB MEASURED VERSUS FIELD OBSERVED Zhongping Lee of the ratio of the backscattering coefficient to the absorption coefficient (or the sum of absorption]. In general, it has been found that reflectance can be well explained (or modeled) using known absorption
Theory and measurements of labyrinth seal coefficients for rotor stability of turbocompressors
NASA Technical Reports Server (NTRS)
Syssmann, H. R.
1987-01-01
The prediction of rotordynamic coefficients for gas seals is achieved with the aid of a two-volume bulk flow model based on turbulent rotationally symmetric 3D flow calculations including swirl flow. Comparison of cross-coupling and damping coefficients with measurements confirm this approach. In particular the theoretically predicted phenomenon that labyrinth damping is retained without inlet swirl is confirmed. This is important for the design of high pressure compressors, where labyrinth damping is a major contribution improving rotor stability. Discrepancies are found when comparing theory with measured direct stiffness and the cross-coupling damping coefficients. First measurements of labyrinth seals on a recently installed test rig operated with water are presented. Since forces are larger than on test stands operated with air and since individual chamber forces are obtained phenomena like inlet effects may be studied.
Rotordynamic coefficients and leakage flow of parallel grooved seals and smooth seals
NASA Technical Reports Server (NTRS)
Nordmann, R.; Dietzen, F. J.; Janson, W.; Frei, A.; Florjancic, S.
1987-01-01
Based on Childs finite length solution for annular plain seals an extension of the bulk flow theory is derived to calculate the rotordynamic coefficients and the leakage flow of seals with parallel grooves in the stator. Hirs turbulent lubricant equations are modified to account for the different friction factors in circumferential and axial direction. Furthermore an average groove depth is introduced to consider the additional circumferential flow in the grooves. Theoretical and experimental results are compared for the smooth constant clearance seal and the corresponding seal with parallel grooves. Compared to the smooth seal the direct and cross-coupled stiffness coefficients as well as the direct damping coefficients are lower in the grooved seal configuration. Leakage is reduced by the grooving pattern.
Alaoui-Ismaili, N. [INSA-Lyon, MATEIS, UMR5510 Villeurbanne, F-69621 (France); Guy, P. [INSA-Lyon, LVA, EA677 Villeurbanne, F-69621 (France); Chassignole, B. [EDF R and D, Moret sur Loing, F77818 (France)
2014-02-18
The aim of this work is to measure the complex elastic tensor and Euler angles in very complex anisotropic media like austenitic steel welds, by inverse problem resolution from experimental data. The obtained experimental characteristics of the anisotropic material will be injected in a FE code developed by EDF enabling the simulation of an actual ultrasonic NDE of welds. The present work aims to provide reliable input data to the 3D future development of the code. In particular, this complex elastic tensor will allow to predict by modeling beam skewing ant attenuation in an austenitic weld. The investigation of such anisotropic media is very complex because of the directional dependency of the elastic stiffness tensor. Then we will discuss the use of a hybrid genetic algorithm to overcome this difficulty. The identification method is based on waveforms spectra reconstruction associated to a physical model describing wave propagation in plates, during underwater measurements. The entire procedure is qualified and validated using simulated data. Moreover, a comparison of the estimated elastic coefficients with literature values and ultrasonic measurements obtained in transmission is also given, at the end of the paper.
NASA Astrophysics Data System (ADS)
Alaoui-Ismaili, N.; Guy, P.; Chassignole, B.
2014-02-01
The aim of this work is to measure the complex elastic tensor and Euler angles in very complex anisotropic media like austenitic steel welds, by inverse problem resolution from experimental data. The obtained experimental characteristics of the anisotropic material will be injected in a FE code developed by EDF enabling the simulation of an actual ultrasonic NDE of welds. The present work aims to provide reliable input data to the 3D future development of the code. In particular, this complex elastic tensor will allow to predict by modeling beam skewing ant attenuation in an austenitic weld. The investigation of such anisotropic media is very complex because of the directional dependency of the elastic stiffness tensor. Then we will discuss the use of a hybrid genetic algorithm to overcome this difficulty. The identification method is based on waveforms spectra reconstruction associated to a physical model describing wave propagation in plates, during underwater measurements. The entire procedure is qualified and validated using simulated data. Moreover, a comparison of the estimated elastic coefficients with literature values and ultrasonic measurements obtained in transmission is also given, at the end of the paper.
Grabovskis, Andris; Marcinkevics, Zbignevs; Rubins, Uldis; Kviesis-Kipge, Edgars
2013-02-01
Currently, photoplethysmography (PPG) is a frequently studied optical blood pulsation detection technique among biophotonic and biomedical researchers due to the fact that it shows high potential for estimating the arterial stiffness (AS). The extraction of diagnostically useful information requires standardized measurement procedure with good repeatability. However, the effects of a crucially important factor-the optimal contact pressure (CP) of the probe-are often ignored. Also, CP values are not reported to evaluate those effects. It is hypothesized that AS estimated from PPG pulse wave 2nd derivative parameter b/a is strongly inconsistent when recorded at nonoptimal probe CP. Our pilot study confirmed this during in vivo PPG recordings from conduit artery sites on five healthy subjects at variable probe CP (0 to 15 kPa) by using 880 nm reflectance type sensor, force transducer, and PPG alternating current (AC) signal pulse area derived optimal CP criterion. The b/a values, calculated from PPG with variable CP, showed variation >300 percent. In contrast, at the optimal CP, the b/a showed high repeatability (coefficient of variability <5 percent). The effect has been explained with exponential pulse pressure-volume relationship model which indicates the optimal CP range. PMID:23377011
Steady state likelihood ratio sensitivity analysis for stiff kinetic Monte Carlo simulations.
Núñez, M; Vlachos, D G
2015-01-28
Kinetic Monte Carlo simulation is an integral tool in the study of complex physical phenomena present in applications ranging from heterogeneous catalysis to biological systems to crystal growth and atmospheric sciences. Sensitivity analysis is useful for identifying important parameters and rate-determining steps, but the finite-difference application of sensitivity analysis is computationally demanding. Techniques based on the likelihood ratio method reduce the computational cost of sensitivity analysis by obtaining all gradient information in a single run. However, we show that disparity in time scales of microscopic events, which is ubiquitous in real systems, introduces drastic statistical noise into derivative estimates for parameters affecting the fast events. In this work, the steady-state likelihood ratio sensitivity analysis is extended to singularly perturbed systems by invoking partial equilibration for fast reactions, that is, by working on the fast and slow manifolds of the chemistry. Derivatives on each time scale are computed independently and combined to the desired sensitivity coefficients to considerably reduce the noise in derivative estimates for stiff systems. The approach is demonstrated in an analytically solvable linear system. PMID:25637970
Kubo Formulas for Second-Order Hydrodynamic Coefficients
Moore, Guy D.; Sohrabi, Kiyoumars A. [Department of Physics, McGill University, 3600 rue University, Montreal, Quebec H3A 2T8 (Canada)
2011-03-25
At second order in gradients, conformal relativistic hydrodynamics depends on the viscosity {eta} and on five additional ''second-order'' hydrodynamical coefficients {tau}{sub {Pi}}, {kappa}, {lambda}{sub 1}, {lambda}{sub 2}, and {lambda}{sub 3}. We derive Kubo relations for these coefficients, relating them to equilibrium, fully retarded three-point correlation functions of the stress tensor. We show that the coefficient {lambda}{sub 3} can be evaluated directly by Euclidean means and does not in general vanish.
Microtubules regulate GEF-H1 in response to extracellular matrix stiffness
Heck, Jessica N.; Ponik, Suzanne M.; Garcia-Mendoza, Maria G.; Pehlke, Carolyn A.; Inman, David R.; Eliceiri, Kevin W.; Keely, Patricia J.
2012-01-01
Breast epithelial cells sense the stiffness of the extracellular matrix through Rho-mediated contractility. In turn, matrix stiffness regulates RhoA activity. However, the upstream signaling mechanisms are poorly defined. Here we demonstrate that the Rho exchange factor GEF-H1 mediates RhoA activation in response to extracellular matrix stiffness. We demonstrate the novel finding that microtubule stability is diminished by a stiff three-dimensional (3D) extracellular matrix, which leads to the activation of GEF-H1. Surprisingly, activation of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathway did not contribute to stiffness-induced GEF-H1 activation. Loss of GEF-H1 decreases cell contraction of and invasion through 3D matrices. These data support a model in which matrix stiffness regulates RhoA through microtubule destabilization and the subsequent release and activation of GEF-H1. PMID:22593214
NASA Astrophysics Data System (ADS)
Chang, Chia-Ming; Keefe, Andrew; Carter, William B.; Henry, Christopher P.; McKnight, Geoff P.
2014-04-01
Structural assemblies incorporating negative stiffness elements have been shown to provide both tunable damping properties and simultaneous high stiffness and damping over prescribed displacement regions. In this paper we explore the design space for negative stiffness based assemblies using analytical modeling combined with finite element analysis. A simplified spring model demonstrates the effects of element stiffness, geometry, and preloads on the damping and stiffness performance. Simplified analytical models were validated for realistic structural implementations through finite element analysis. A series of complementary experiments was conducted to compare with modeling and determine the effects of each element on the system response. The measured damping performance follows the theoretical predictions obtained by analytical modeling. We applied these concepts to a novel sandwich core structure that exhibited combined stiffness and damping properties 8 times greater than existing foam core technologies.
Accurate spring constant calibration for very stiff atomic force microscopy cantilevers
Grutzik, Scott J.; Zehnder, Alan T. [Field of Theoretical and Applied Mechanics, Cornell University, Ithaca, New York 14853 (United States)] [Field of Theoretical and Applied Mechanics, Cornell University, Ithaca, New York 14853 (United States); Gates, Richard S.; Gerbig, Yvonne B.; Smith, Douglas T.; Cook, Robert F. [Nanomechanical Properties Group, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)] [Nanomechanical Properties Group, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)
2013-11-15
There are many atomic force microscopy (AFM) applications that rely on quantifying the force between the AFM cantilever tip and the sample. The AFM does not explicitly measure force, however, so in such cases knowledge of the cantilever stiffness is required. In most cases, the forces of interest are very small, thus compliant cantilevers are used. A number of methods have been developed that are well suited to measuring low stiffness values. However, in some cases a cantilever with much greater stiffness is required. Thus, a direct, traceable method for calibrating very stiff (approximately 200 N/m) cantilevers is presented here. The method uses an instrumented and calibrated nanoindenter to determine the stiffness of a reference cantilever. This reference cantilever is then used to measure the stiffness of a number of AFM test cantilevers. This method is shown to have much smaller uncertainty than previously proposed methods. An example application to fracture testing of nanoscale silicon beam specimens is included.
Lower limb joint kinetics and ankle joint stiffness in the sprint start push-off
Laura Charalambous; Gareth Irwin; Ian N. Bezodis; David Kerwin
2011-01-01
Sprint push-off technique is fundamental to sprint performance and joint stiffness has been identified as a performance-related variable during dynamic movements. However, joint stiffness for the push-off and its relationship with performance (times and velocities) has not been reported. The aim of this study was to quantify and explain lower limb net joint moments and mechanical powers, and ankle stiffness
Lower limb joint kinetics and ankle joint stiffness in the sprint start push-off
Laura Charalambous; Gareth Irwin; Ian N. Bezodis; David Kerwin
2012-01-01
Sprint push-off technique is fundamental to sprint performance and joint stiffness has been identified as a performance-related variable during dynamic movements. However, joint stiffness for the push-off and its relationship with performance (times and velocities) has not been reported. The aim of this study was to quantify and explain lower limb net joint moments and mechanical powers, and ankle stiffness
Y. S. Chen; C. C. Chiu; Y. D. Cheng
2010-01-01
The stiffness of various geometric designs of aerostatic journal bearings for high-speed spindles was investigated under different operating conditions. First, the stiffness of the front and rear journal bearings was evaluated experimentally using the relationship of force and displacement at different supply pressures (6–9bar). A numerical model was then developed to simulate journal-bearing stiffness under the same pressure range to
Multifunctional piezoelectric stiffness\\/energy for monitoring the health of structures
Kelah Wakha; Majeed A. Majed; Abhijit Dasgupta; Darryll J. Pines
2003-01-01
A new mechanical multifunctional dual-stiffness sensor for in-situ real-time stiffness and energy density measurements was developed at the University of Maryland. This sensor is composed of 2 sub-sensors a stiff and compliant subsensor. The sensor has the ability to predict the elastic field of a given host structure based on the strain state of the two sub-sensors integrated into the
An AFM-based stiffness clamp for dynamic control of rigidity.
Webster, Kevin D; Crow, Ailey; Fletcher, Daniel A
2011-01-01
Atomic force microscopy (AFM) has become a powerful tool for measuring material properties in biology and imposing mechanical boundary conditions on samples from single molecules to cells and tissues. Constant force or constant height can be maintained in an AFM experiment through feedback control of cantilever deflection, known respectively as a 'force clamp' or 'position clamp'. However, stiffness, the third variable in the Hookean relation F?=?kx that describes AFM cantilever deflection, has not been dynamically controllable in the same way. Here we present and demonstrate a 'stiffness clamp' that can vary the apparent stiffness of an AFM cantilever. This method, employable on any AFM system by modifying feedback control of the cantilever, allows rapid and reversible tuning of the stiffness exposed to the sample in a way that can decouple the role of stiffness from force and deformation. We demonstrated the AFM stiffness clamp on two different samples: a contracting fibroblast cell and an expanding polyacrylamide hydrogel. We found that the fibroblast, a cell type that secretes and organizes the extracellular matrix, exhibited a rapid, sub-second change in traction rate (dF/dt) and contraction velocity (dx/dt) in response to step changes in stiffness between 1-100 nN/µm. This response was independent of the absolute contractile force and cell height, demonstrating that cells can react directly to changes in stiffness alone. In contrast, the hydrogel used in our experiment maintained a constant expansion velocity (dx/dt) over this range of stiffness, while the traction rate (dF/dt) changed with stiffness, showing that passive materials can also behave differently in different stiffness environments. The AFM stiffness clamp presented here, which is applicable to mechanical measurements on both biological and non-biological samples, may be used to investigate cellular mechanotransduction under a wide range of controlled mechanical boundary conditions. PMID:21408137
Stiffness analysis for effective peg-in\\/out-hole tasks using multi-fingered robot hands
Byoung-Ho Kim; Byung-Ju Yi; Il Hong Suh; Sang-Rok Oh
2000-01-01
This paper deals with stiffness analysis for effective peg-in\\/out-hole tasks using multifingered robot hand without inter-finger coupling. We first observe the fact that some coupling stiffness elements cannot be planned arbitrary. Then, we analyze the conditions of the specified stiffness matrix in the operational space to successfully and more effectively achieve the given peg-in\\/out-hole tasks. It is concluded that the
Stiffness Control and Transformation for Robotic Systems with Coordinate and Non-Coordinate Bases
Yanmei Li; Shih-feng Chen; Imin Kao
2002-01-01
In this paper, the application of the conservative congruence transformation (CCT) to the stiffness mapping between non-coordinate basis and coordinate basis systems is studied and presented. Through the stiffness transformation between the 2 degree-of-freedom cylindrical and joint spaces, we illustrate that the CCT can be applied either directly or indirectly to the stiffness transformation between any two systems with either
Geometrical method for modeling of asymmetric 6×6 Cartesian stiffness matrix
Shih-Feng Chen; Imin Kaot
2000-01-01
In this paper, we study the 6×6 Cartesian stiffness matrices of conservative systems using the method of changing basis in differential geometry of the motion of the rigid body. We show that the stiffness matrix is symmetric at the unloaded equilibrium configuration. When the system is subjected to external loads, the 6×6 Cartesian stiffness matrix becomes asymmetric. The skew-symmetric part
A stiffness analysis for CaPaMan (CassinoParallel Manipulator)
Marco Ceccarelli; Giuseppe Carbone
2002-01-01
In this paper the 3 d.o.f. parallel manipulator, named as CaPaMan (Cassino Parallel Manipulator), is analysed in terms of stiffness characteristics. A formulation is presented to deduce the stiffness matrix as a function of the most important stiffness parameters of the CaPaMan architecture. The specific design of CaPaMan, which has been designed and built at the Laboratory of Robotics and
Stiffness Matrix Analysis and Synthesis for Pre-Loaded Planar Structures
Hyun Geun Yu; Rodney G. Roberts
2006-01-01
The compliance\\/stiffness of a robotic mechanism is usually modeled by a 6 by 6 symmetric positive definite matrix at an equilibrium point using screw theory. When an external wrench is exerted on the mechanism and the mechanism moves away from its equilibrium, the modeled compliance\\/stiffness matrix becomes non-symmetric. In this article, the authors derive a non-symmetric stiffness matrix for a
A stiffness analysis for CaPaMan (Cassino Parallel Manipulator)
Marco Ceccarelli; Giuseppe Carbone
2002-01-01
In this paper the 3 d.o.f. parallel manipulator, named as CaPaMan (Cassino Parallel Manipulator), is analysed in terms of stiffness characteristics. A formulation is presented to deduce the stiffness matrix as a function of the most important stiffness parameters of the CaPaMan architecture. The specific design of CaPaMan, which has been designed and built at the Laboratory of Robotics and
Stiffness Optimization of a 3DOF Parallel Kinematic Machine Using Particle Swarm Optimization
Qingsong Xu; Yangmin Li
2006-01-01
In this paper, the architectural parameters optimiza- tion of a three-prismatic-universal-universal (3-PUU) parallel kinematic machine (PKM) with three translational degree-of- freedom (DOF) is performed using the efficient particle swarm optimization (PSO) to achieve the optimum stiffness charac- teristics. Based on the stiffness matrix derived previously, the minimum stiffness over a cubic usable workspace is considered as a performance index since
Ritz method for transient response in systems having unsymmetric stiffness
NASA Technical Reports Server (NTRS)
Butler, Thomas G.
1989-01-01
The DMAP coding was automated to such an extent by using the device of bubble vectors, that it is useable for analyses in its present form. This feasibility study demonstrates that the Ritz Method is so compelling as to warrant coding its modules in FORTRAN and organizing the resulting coding into a new Rigid Format. Even though this Ritz technique was developed for unsymmetric stiffness matrices, it offers advantages to problems with symmetric stiffnesses. If used for the symmetric case the solution would be simplified to one set of modes, because the adjoint would be the same as the primary. Its advantage in either type of symmetry over a classical eigenvalue modal expansion is that information density per Ritz mode is far richer than per eigenvalue mode; thus far fewer modes would be needed for the same accuracy and every mode would actively participate in the response. Considerable economy can be realized in adapting Ritz vectors for modal solutions. This new Ritz capability now makes NASTRAN even more powerful than before.
Confinement and controlling the effective compressive stiffness of carbyne.
Kocsis, Ashley J; Yedama, Neta Aditya Reddy; Cranford, Steven W
2014-08-22
Carbyne is a one-dimensional chain of carbon atoms, consisting of repeating sp-hybridized groups, thereby representing a minimalist molecular rod or chain. While exhibiting exemplary mechanical properties in tension (a 1D modulus on the order of 313 nN and a strength on the order of 11 nN), its use as a structural component at the molecular scale is limited due to its relative weakness in compression and the immediate onset of buckling under load. To circumvent this effect, here, we probe the effect of confinement to enhance the mechanical behavior of carbyne chains in compression. Through full atomistic molecular dynamics, we characterize the mechanical properties of a free (unconfined chain) and explore the effect of confinement radius (R), free chain length (L) and temperature (T) on the effective compressive stiffness of carbyne chains and demonstrate that the stiffness can be tuned over an order of magnitude (from approximately 0.54 kcal mol(-1) Å(2) to 46 kcal mol(-1) Å(2)) by geometric control. Confinement may inherently stabilize the chains, potentially providing a platform for the synthesis of extraordinarily long chains (tens of nanometers) with variable compressive response. PMID:25073433
Molecular Dynamics Study of Stiffness in Polystyrene and Polyethylene
Hamed Nazarpourfard; Mahdi Ahmadi Borji
2015-04-26
In this paper, we have studied polystyrene (PS) and polyethylene (PE) stiffness by 3-dimensional Langevin Molecular Dynamics simulation. Hard polymers have a very small bending, and thus, their end-to-end distance is more than soft polymers. Quantum dot lasers can be established as colloidal particles dipped in a liquid and grafted by polymer brushes to maintain the solution. Here by a study on molecular structures of PS and PE, we show that the principle reason lies on large phenyl groups around the backbone carbons of PS, rather than a PE with Hydrogen atoms. Our results show that the mean radius of PS random coil is more than PE which directly affects the quantum dot maintenance. In addition, effect of temperature increase on the mean radius is investigated. Our results show that by increasing temperature, both polymers tend to lengthen, and at all temperatures a more radius is predicted for PS rather than PE, but interestingly, with a difference in short and long chains. We show that stiffness enhancement is not the same at short and long polymers and the behavior is very different. Our results show a good consonance with both experimental and theoretical studies.
Mechanosensitive Kinases Regulate Stiffness-Induced Cardiomyocyte Maturation
Young, Jennifer L.; Kretchmer, Kyle; Ondeck, Matthew G.; Zambon, Alexander C.; Engler, Adam J.
2014-01-01
Cells secrete and assemble extracellular matrix throughout development, giving rise to time-dependent, tissue-specific stiffness. Mimicking myocardial matrix stiffening, i.e. ~10-fold increase over 1 week, with a hydrogel system enhances myofibrillar organization of embryonic cardiomyocytes compared to static hydrogels, and thus we sought to identify specific mechanosensitive proteins involved. Expression and/or phosphorylation state of 309 unique protein kinases were examined in embryonic cardiomyocytes plated on either dynamically stiffening or static mature myocardial stiffness hydrogels. Gene ontology analysis of these kinases identified cardiogenic pathways that exhibited time-dependent up-regulation on dynamic versus static matrices, including PI3K/AKT and p38 MAPK, while GSK3?, a known antagonist of cardiomyocyte maturation, was down-regulated. Additionally, inhibiting GSK3? on static matrices improved spontaneous contraction and myofibril organization, while inhibiting agonist AKT on dynamic matrices reduced myofibril organization and spontaneous contraction, confirming its role in mechanically-driven maturation. Together, these data indicate that mechanically-driven maturation is at least partially achieved via active mechanosensing at focal adhesions, affecting expression and phosphorylation of a variety of protein kinases important to cardiomyogenesis. PMID:25236849
Negative stiffness induced by shear along wavy interfaces
NASA Astrophysics Data System (ADS)
Anderson, Erin; Li, Ruizhi; Chew, Huck Beng
2014-02-01
The extension of an elastic body almost always leads to mechanical tension in the stretching direction. Here, we report an unusual phenomenon of global mechanical compression in the stretching direction of an elastic body containing sinusoidal wavy interfaces. When the elastic body with a wavy interface is subjected to tensile loading, the local stress state along the interface is mixed-mode. Finite element simulations show that the resistance of the interface to shear-slip locks the interface together, and generates a moment couple which rotates the interface. Once the local adhesive shear strength of the interface is reached, the interface slips and separates. Then, the rotated interface triggers a restoring moment couple which releases the stored elastic energy. The structure subsequently undergoes global compression in the stretching direction until the interface completely separates. This moment-couple-induced internal energy storage and release mechanism leads to a material structure that exhibits high initial strength and toughness, followed by post-peak compliant softening with negative stiffness. This structural negative stiffness behavior is closely-tied with the ability of the interface to store and release energy by rotation, and is also exhibited by polycrystalline structures where grain rotation is possible.
Targeting Fold Stiffness to Design Enhanced Origami Structures
NASA Astrophysics Data System (ADS)
Buskohl, Philip; Bazzan, Giorgio; Abbott, Andrew; Durstock, Michael; Vaia, Richard
2014-03-01
Structures with adaptive geometry are increasingly of interest for actuation, sensing and packaging applications. Origami structures, by definition, can ``shape-shift'' between multiple geometric configurations that are predefined by a pattern of folds. Plastic deformation and local failure at the fold lines transform an originally homogenous material into a grid with locally tailored mechanical properties that bias the response of the overall structure to external loading. Typically, origami structures focus on uniformly stiff fold lines with rigid facets. In this study, we discuss how localized variations in stiffness can influence global properties, including energy budget to transition from flat to folded structure, the preferred path through configuration space, and the final mechanical response of the folded architecture. A simple, bi-stable origami fold pattern is laser machined into polypropylene sheets of different compliance and the critical load of the transition is measured. We model the structure as a truss with bar elongation, folding, and facet bending in order to predict ways to enhance or mitigate the critical load. Targeting local folding properties to modify global performance directly extends to the analysis of more complex architectures.
Efficient semi-implicit schemes for stiff systems
NASA Astrophysics Data System (ADS)
Nie, Qing; Zhang, Yong-Tao; Zhao, Rui
2006-05-01
When explicit time discretization schemes are applied to stiff reaction-diffusion equations, the stability constraint on the time step depends on two terms: the diffusion and the reaction. The part of the stability constraint due to diffusion can be totally removed if the linear diffusions are treated exactly using integration factor (IF) or exponential time differencing (ETD) methods. For systems with severely stiff reactions, those methods are not efficient because the reaction terms in IF or ETD are still approximated with explicit schemes. In this paper, we introduce a new class of semi-implicit schemes, which treats the linear diffusions exactly and explicitly, and the nonlinear reactions implicitly. A distinctive feature of the scheme is the decoupling between the exact evaluation of the diffusion terms and implicit treatment of the nonlinear reaction terms. As a result, the size of the nonlinear system arising from the implicit treatment of the reactions is independent of the number of spatial grid points; it only depends on the number of original equations, unlike the case in which standard implicit temporal schemes are directly applied to the reaction-diffusion system. The stability region for this class of methods is much larger than existing methods using an explicit treatment of reaction terms. In particular, the one with second order accuracy is unconditionally linearly stable with respect to both diffusion and reaction. Direct numerical simulations on test equations, as well as morphogen systems from developmental biology, show the new semi-implicit schemes are efficient, robust and accurate.
Stroka, Kimberly M.
2011-01-01
A vast amount of work has been dedicated to the effects of shear flow and cytokines on leukocyte transmigration. However, no studies have explored the effects of substrate stiffness on transmigration. Here, we investigated important aspects of endothelial cell contraction-mediated neutrophil transmigration using an in vitro model of the vascular endothelium. We modeled blood vessels of varying mechanical properties using fibronectin-coated polyacrylamide gels of varying physiologic stiffness, plated with human umbilical vein endothelial cell (HUVEC) monolayers, which were activated with tumor necrosis factor-?. Interestingly, neutrophil transmigration increased with increasing substrate stiffness below the endothelium. HUVEC intercellular adhesion molecule-1 expression, stiffness, cytoskeletal arrangement, morphology, and cell-substrate adhesion could not account for the dependence of transmigration on HUVEC substrate stiffness. We also explored the role of cell contraction and observed that large holes formed in endothelium on stiff substrates several minutes after neutrophil transmigration reached a maximum. Further, suppression of contraction through inhibition of myosin light chain kinase normalized the effects of substrate stiffness by reducing transmigration and eliminating hole formation in HUVECs on stiff substrates. These results provide strong evidence that neutrophil transmigration is regulated by myosin light chain kinase-mediated endothelial cell contraction and that this event depends on subendothelial cell matrix stiffness. PMID:21652678
Stiff Man Syndrome: A Diagnostic Dilemma in a Young Female with Diabetes Mellitus and Thyroiditis
Enuh, Hilary; Park, Michael; Ghodasara, Arjun; Arsura, Edward; Nfonoyim, Jay
2014-01-01
Stiff Person Syndrome (SPS), is a very rare neuroimmunologic disorder characterized by progressive muscle pain, rigidity, stiffness, and spasms. It can be very debilitating if misdiagnosed or not recognized in time. Herein we discuss a case of a female in her 20s who presented with an unsteady gait, lower extremity weakness, persistent leg pain, and stiffness few weeks after uncomplicated childbirth. She has type 1 diabetes mellitus (DM) and was diagnosed with thyroiditis in the course of her illness. The triad of thyroiditis, DM, and stiffness with normal neuroimaging in a young female patient is an unusual occurrence. PMID:25525403
An update on the role of adipokines in arterial stiffness and hypertension.
Sabbatini, Andréa R; Fontana, Vanessa; Laurent, Stephane; Moreno, Heitor
2015-03-01
Adipokines are hormones produced by adipocytes and have been involved in multiple pathologic pathways, including inflammatory and cardiovascular complications in essential hypertension. Arterial stiffness is a frequent vascular complication that represents increased cardiovascular risk in hypertensive patients. Adipokines, such as adiponectin, leptin and resistin, might be implicated in hypertension, as well as in vascular alterations associated with this condition. Arterial stiffness has proven to be a predictor of cardiovascular events. Obesity and target-organ damage such as arterial stiffness are features associated with hypertension. This review aims to update the association between adipokines and arterial stiffness in essential and resistant hypertension (RHTN). PMID:25502905
Review of ‘the potential role of arterial stiffness in the pathogenesis of Alzheimer’s disease’
Hughes, Timothy M; Craft, Suzanne; Lopez, Oscar L
2015-01-01
SUMMARY Arterial stiffness is emerging as an important risk marker for poor brain aging and dementia through its associations with cerebral small vessel disease, stroke, ?-amyloid deposition, brain atrophy and cognitive impairment. Arterial stiffness directly relates the detrimental effects of hypertension on peripheral organs with dire consequences for the extensive microvasculature structure of the kidneys and brain. In this review, we discuss the evidence linking arterial stiffness, hypertension and brain structural abnormalities in older adults. In particular, we discuss the potential mechanisms linking arterial stiffness to brain ?-amyloid deposition and dementia and potential therapeutic strategies to prevent hypertension’s adverse effects on the brain. PMID:25894876
Stiffness Properties for Dynamic Modeling of Composite Graphite-Epoxy Cylindrical Orthotropic Shells
NASA Technical Reports Server (NTRS)
Tolbert, R. N.
1983-01-01
Traditional composite lamination theory was used to predict composite graphite-epoxy laminate stiffnesses for comparison to quasi-experimental stiffnesses developed from cylindrical bottle pressure testing. Stiffness sensitivities were examined for variations in constituent materials and geometric properties. The material component interactions examined were the fiber longitudinal and transverse Young's modulus, the fiber shear modulus and primary Poisson's ratio, the resin Young's modulus, shear modulus, and Poisson's ratio. The geometric variation of the helical winding angle was also examined. Two computer programs were written to generate the data used to demonstrate the stiffness variations.
Stiff Temperature Profiles in JT-60U ELMy H-mode Plasmas
D.R. Mikkelsen; H. Urano; H. Shirai; T. Takizuka; Y. Kamada; T. Hatae; Y. Koide; N. Asakura; T. Fujita; T. Fukuda; S. Ide; A. Isayama; Y. Kawano; O. Naito; Y. Sakamoto
2001-10-16
The 'stiffness' of thermal transport in ELMy H-modes [edge localized high-confinement modes] is examined in a series of carefully chosen JT-60U plasmas, and measured temperatures are compared with the predictions of several transport models. A heating power scan with constant T(subscript ''ped''), a scan of pedestal temperature, T(subscript ''ped''), with constant heating power, and an on-axis/off-axis heating comparison are presented. In the power scan a 45% increase in heating (and a 12% density rise) produces an approximately fixed core temperature profile in a group of five plasmas with the same pedestal temperature. With fixed heating power, we find that a 30-40% increase in T(subscript ''ped'') is associated with similar increases in core temperature. Heating in the deep core is varied by employing different groups of neutral beams that deposit their power near the magnetic axis and farther from the axis. In these plasmas, on-axis heating produces slightly more peaked temperature profiles, although they have 60% more heating power inside r = a/2. Transport models are tested by solving the power balance equations to predict temperatures, which are then compared to the measurements. Predictions of the RLWB and IFS/PPPL models generally agree with the measured temperatures outside r approximately 0.3a, but the multimode model uniformly predicts temperatures that are too high except in the central region. Tests based on these discharges are not able to discriminate between the transport models of varying stiffness, so we conclude that larger changes are needed in the P(subscript ''heat'') and T(subscript ''ped'') scans.