NASA Astrophysics Data System (ADS)
Nemov, A. S.; Boso, D. P.; Voynov, I. B.; Borovkov, A. I.; Schrefler, B. A.
2010-05-01
Superconducting coils are one of the key technical solutions used for generation of high magnetic field in modern tokamaks. Nb 3Sn superconductivity depends not only on temperature and magnetic field as e.g. NbTi, but also on the strain state of the strands inside the conductor. It is hence very important to be able to predict the mechanical deformations due to manufacturing processes and operating conditions. The conductors for ITER, the International Thermonuclear Experimental Reactor currently under construction, have a complex structure that makes analytical estimations of stiffness applicable only for the first cabling stages. In this work, a wide range of numerical simulations has been performed, by using several types of finite element models. This paper shows some analytical estimations for stretching and twisting and compares them with the numerical results of the different models. Some comparisons with experimental tests are also presented. Furthermore, it is shown that direct finite element analyses are compulsory for higher cable stages, but need the knowledge of the initial configuration as precise as possible for meaningful simulations. This problem is also addressed in this paper.
Elastic-Stiffness Coefficients of Titanium Diboride
Ledbetter, Hassel; Tanaka, Takaho
2009-01-01
Using resonance ultrasound spectroscopy, we measured the monocrystal elastic-stiffness coefficients, the Voigt Cij, of TiB2. With hexagonal symmetry, TiB2 exhibits five independent Cij: C11, C33, C44, C12, C13. Using Voigt-Reuss-Hill averaging, we converted these monocrystal values to quasiisotropic (polycrystal) elastic stiffnesses. Briefly, we comment on effects of voids. From the Cij, we calculated the Debye characteristic temperature, the Grüneisen parameter, and various sound velocities. Our study resolves the enormous differences between two previous reports of TiB2’s Cij.
Tilting pad journal bearings - Measured and predicted stiffness coefficients
Parkins, D.W.; Horner, D. Michell Bearings, Newcastle-upon-Tyne )
1993-07-01
This paper presents measured and calculated characteristics of a tilting pad journal bearing suitable for high speed machinery. Descriptions are given of the experimental techniques used with this variety of bearing and the theoretical model for predicting performance. Measured values of pad temperature, eccentricity, attitude angle, and the four stiffness coefficients are given for a range of loads and rotational speeds. Data are given for both load on pad and between pad configurations, the two principal loading arrangements. Comparisons are made between the measured and predicted bearing temperatures and stiffness coefficients over a wide range of values. 11 refs.
Tilting pad journal bearings - Measured and predicted stiffness coefficients
NASA Astrophysics Data System (ADS)
Parkins, D. W.; Horner, D.
1993-07-01
This paper presents measured and calculated characteristics of a tilting pad journal bearing suitable for high speed machinery. Descriptions are given of the experimental techniques used with this variety of bearing and the theoretical model for predicting performance. Measured values of pad temperature, eccentricity, attitude angle, and the four stiffness coefficients are given for a range of loads and rotational speeds. Data are given for both load on pad and between pad configurations, the two principal loading arrangements. Comparisons are made between the measured and predicted bearing temperatures and stiffness coefficients over a wide range of values.
Experimental and theoretical rotordynamic stiffness coefficients for a three-stage brush seal
NASA Astrophysics Data System (ADS)
Pugachev, A. O.; Deckner, M.
2012-08-01
Experimental and theoretical results are presented for a multistage brush seal. Experimental stiffness is obtained from integrating circumferential pressure distribution measured in seal cavities. A CFD analysis is used to predict seal performance. Bristle packs are modeled by the porous medium approach. Leakage is predicted well by the CFD method. Theoretical stiffness coefficients are in reasonable agreement with the measurements. Experimental results are also compared with a three-teeth-on-stator labyrinth seal. The multistage brush seal gives about 60% leakage reduction over the labyrinth seal. Rotordynamic stiffness coefficients are also improved: the brush seal has positive direct stiffness and smaller cross-coupled stiffness.
Calculation of stiffness and damping coefficients for elastically supported gas foil bearings
NASA Technical Reports Server (NTRS)
Peng, J.-P.; Carpino, M.
1993-01-01
The stiffness and damping coefficients of an elastically supported gas foil bearing are calculated. A perfect gas is used as the lubricant, and its behavior is described by the Reynolds equation. The structural model consists only of an elastic foundation. The fluid equations and the structural equations are coupled. A perturbation method is used to obtain the linearized dynamic coefficient equations. A finite difference formulation has been developed to solve for the four stiffness and the four damping coefficients. The effect of the bearing compliance on the dynamic coefficients is discussed in this paper.
NASA Technical Reports Server (NTRS)
Della-Corte, Christopher
2012-01-01
Foil gas bearings are a key technology in many commercial and emerging oilfree turbomachinery systems. These bearings are nonlinear and have been difficult to analytically model in terms of performance characteristics such as load capacity, power loss, stiffness, and damping. Previous investigations led to an empirically derived method to estimate load capacity. This method has been a valuable tool in system development. The current work extends this tool concept to include rules for stiffness and damping coefficient estimation. It is expected that these rules will further accelerate the development and deployment of advanced oil-free machines operating on foil gas bearings.
NASA Technical Reports Server (NTRS)
DellaCorte, Christopher
2010-01-01
Foil gas bearings are a key technology in many commercial and emerging Oil-Free turbomachinery systems. These bearings are non-linear and have been difficult to analytically model in terms of performance characteristics such as load capacity, power loss, stiffness and damping. Previous investigations led to an empirically derived method, a rule-of-thumb, to estimate load capacity. This method has been a valuable tool in system development. The current paper extends this tool concept to include rules for stiffness and damping coefficient estimation. It is expected that these rules will further accelerate the development and deployment of advanced Oil-Free machines operating on foil gas bearings
Generalized Coefficients for Hopf Cyclic Cohomology
NASA Astrophysics Data System (ADS)
Hassanzadeh, Mohammad; Kucerovsky, Dan; Rangipour, Bahram
2014-09-01
A category of coefficients for Hopf cyclic cohomology is defined. It is shown that this category has two proper subcategories of which the smallest one is the known category of stable anti Yetter-Drinfeld modules. The middle subcategory is comprised of those coefficients which satisfy a generalized SAYD condition depending on both the Hopf algebra and the (co)algebra in question. Some examples are introduced to show that these three categories are different. It is shown that all components of Hopf cyclic cohomology work well with the new coefficients we have defined.
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.
NASA Astrophysics Data System (ADS)
Wei, Kai; Chen, Haosen; Pei, Yongmao; Fang, Daining
2016-01-01
The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CTEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications.
Generalized power-law stiffness model for nonlinear dynamics of in-plane cable networks
NASA Astrophysics Data System (ADS)
Giaccu, Gian Felice; Caracoglia, Luca
2013-04-01
Cross-ties are used for mitigating stay-cable vibration, induced by wind and wind-rain on cable-stayed bridges. In-plane cable networks are obtained by connecting the stays by transverse cross-ties. While taut-cable theory has been traditionally employed for simulating the dynamics of cable networks, the use of a nonlinear restoring-force discrete element in each cross-tie has been recently proposed to more realistically replicate the network vibration when snapping or slackening of the restrainer may be anticipated. The solution to the free-vibration dynamics can be determined by "equivalent linearization method". In an exploratory study by the authors a cubic-stiffness spring element, in parallel with a linear one, was used to analyze the restoring-force effect in a cross-tie on the nonlinear dynamics of two simplified systems. This preliminary investigation is generalized in this paper by considering a power-law stiffness model with a generic integer exponent and applied to a prototype network installed on an existing bridge. The study is restricted to the fundamental mode and some of the higher ones. A time-domain lumped-mass algorithm is used for validating the equivalent linearization method. For the prototype network with quadratic-stiffness spring and a positive stiffness coefficient, a stiffening effect is observed, with a ten percent increment in the equivalent frequency for the fundamental mode. Results also show dependency on vibration amplitude. For higher modes the equivalent nonlinear effects can be responsible for an alteration of the linear mode shapes and a transition from a "localized mode" to a "global mode".
Mayer, O; Seidlerová, J; Wohlfahrt, P; Filipovský, J; Vaněk, J; Cífková, R; Windrichová, J; Topolčan, O; Knapen, M H J; Drummen, N E A; Vermeer, C
2016-07-01
Matrix Gla protein (MGP), a natural inhibitor of calcification, strongly correlates with the extent of coronary calcification. Vitamin K is the essential cofactor for the activation of MGP. The nonphosphorylated-uncarboxylated isoform of MGP (dp-ucMGP) reflects the status of this vitamin. We investigated whether there is an association between dp-ucMGP and stiffness of elastic and muscular-type large arteries in a random sample from the general population. In a cross-sectional design, we analyzed 1087 subjects from the Czech post-MONICA study. Aortic and femoro-popliteal pulse wave velocities (PWVs) were measured using a Sphygmocor device. Dp-ucMGP concentrations were assessed in freshly frozen samples by enzyme-linked immunosorbent assay methods using the InaKtif MGP iSYS pre-commercial kit developed by IDS and VitaK. Aortic PWV significantly (P<0.0001) increased across the dp-ucMGP quartiles. After adjustment for all potential confounders, aortic PWV independently correlated with dp-ucMGP (with beta coefficient (s.d.) 11.61 (5.38) and P-value=0.031). In a categorized manner, subjects in the top quartile of dp-ucMGP (⩾ 671 pmol l(-1)) had a higher risk of elevated aortic PWV, with corresponding adjusted odds ratio (95% confidence interval) 1.73 (1.17-2.5). In contrast, no relation between dp-ucMGP and femoro-popliteal PWV was found. In conclusion, increased dp-ucMGP, which is a circulating biomarker of vitamin K status and vascular calcification, is independently associated with aortic stiffness, but not with stiffness of distal muscular-type arteries. PMID:26016598
Generalized skew coefficients for flood-frequency analysis in Minnesota
Lorenz, D.L.
1997-01-01
This report presents an evaluation of generalized skew coefficients used in flood-frequency analysis. Station skew coefficients were computed for 267 long-term stream-gaging stations in Minnesota and the surrounding states of Iowa, North and South Dakota, Wisconsin, and the provinces of Manitoba and Ontario, Canada. Generalized skew coefficients were computed from station skew coefficients using a locally weighted regression technique. The resulting regression trend surface was the generalized skew coefficient map, except for the North Shore area, and has a mean square error of 0.182.
Dynamic stiffness matrix of a rectangular plate for the general case
NASA Astrophysics Data System (ADS)
Banerjee, J. R.; Papkov, S. O.; Liu, X.; Kennedy, D.
2015-04-01
The dynamic stiffness matrix of a rectangular plate for the most general case is developed by solving the bi-harmonic equation and finally casting the solution in terms of the force-displacement relationship of the freely vibrating plate. Essentially the frequency dependent dynamic stiffness matrix of the plate when all its sides are free is derived, making it possible to achieve exact solution for free vibration of plates or plate assemblies with any boundary conditions. Previous research on the dynamic stiffness formulation of a plate was restricted to the special case when the two opposite sides of the plate are simply supported. This restriction is quite severe and made the general purpose application of the dynamic stiffness method impossible. The theory developed in this paper overcomes this long-lasting restriction. The research carried out here is basically fundamental in that the bi-harmonic equation which governs the free vibratory motion of a plate in harmonic oscillation is solved in an exact sense, leading to the development of the dynamic stiffness method. It is significant that the ingeniously sought solution presented in this paper is completely general, covering all possible cases of elastic deformations of the plate. The Wittrick-Williams algorithm is applied to the ensuing dynamic stiffness matrix to provide solutions for some representative problems. A carefully selected sample of mode shapes is also presented.
Linear equations in general purpose codes for stiff ODEs
Shampine, L. F.
1980-02-01
It is noted that it is possible to improve significantly the handling of linear problems in a general-purpose code with very little trouble to the user or change to the code. In such situations analytical evaluation of the Jacobian is a lot cheaper than numerical differencing. A slight change in the point at which the Jacobian is evaluated results in a more accurate Jacobian in linear problems. (RWR)
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
Inhomogeneous generalizations of Bianchi Type VIh universes with stiff perfect fluid and radiation
NASA Astrophysics Data System (ADS)
Roy, S. R.; Prasad, A.
1995-03-01
Families of inhomogeneous models filled with a stiff perfect fluid and radiation have been derived in which there is no flow of total momentum. The models are generalizations of those of Bianchi Type VIh and are discussed for some particular forms of the arbitrary functions appearing in them.
Nagy, P.B.; Nayfeh, A.H.
1995-09-25
The surface stiffness of a fluid-saturated porous solid is defined as the ratio between a small change in capillary pressure and the average displacement of the boundary due to the resulting rise or fall of the fluid level in the pore channels. When the surface pores are structurally open, the surface stiffness is entirely due to the stiffness of the microscopic fluid membranes extended by capillary forces over the surface pores. Due to interfacial tension between the immiscible wetting fluid in the pores and nonwetting fluid (air) above the surface, essentially closed-pore boundary conditions can prevail at the interface. It has recently been shown that the surface stiffness of a porous material containing cylindrical pores can be calculated simply as the surface tension of the saturating fluid divided by the static permeability of the porous solid [P. B. Nagy, Appl. Phys. Lett. {bold 60}, 2735 (1992)]. In this letter, we show that the same simple relationship can be generalized for the surface stiffness of fluid-saturated porous media containing parallel prismatic pore channels of any number, size, or shape. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Warm Gauge-Flation with General Dissipative Coefficient
NASA Astrophysics Data System (ADS)
Sharif, M.; Saleem, Rabia; Mohsaneen, Sidra
2016-07-01
In this work, we study the effects of generalized dissipative coefficient on the slow-roll inflation driven by non-Abelian gauge field minimally coupled to gravity. The dynamics of warm intermediate and logamediate inflationary models during weak and strong dissipative regimes is analyzed. In both cases, we explore effective scalar potential, slow-roll parameters, scalar and tensor power spectra, scalar spectral index and tensor to scalar ratio under slow-roll conditions. We conclude that our gauge-flationary model with generalized dissipative coefficient remains consistent with the recent data for dissipative parameter m = 3 and m = 1 for weak and strong dissipative eras, respectively.
NASA Technical Reports Server (NTRS)
Thomson, Robert G.
1959-01-01
A study has been made of the effects of varying the shape, solidity, and heat-transfer coefficient of thin wings with regard to their influence on the torsional-stiffness reduction induced by aerodynamic heating. The variations in airfoil shape include blunting, flattening, and combined blunting and flattening of a solid wing of symmetrical double-wedge cross section. Hollow double-wedge wings of constant skin thickness with and without internal webs also are considered. The effects of heat-transfer coefficients appropriate for laminar and turbulent flow are investigated in addition to a step transition along the chord from a lower to a higher constant value of heat-transfer coefficient. From the results given it is concluded that the flattening of a solid double wedge decreases the reduction in torsional stiffness while slight degrees of blunting increase the loss. The influence of chordwise variations in heat-transfer coefficient due to turbulent and laminar boundary-layer flow on the torsional stiffness of solid wings is negligible. The effect of a step transition in heat-transfer coefficient along the chord of a solid wing can, however, become appreciable. The torsional-stiffness reduction of multiweb and hollow double-wedge wings is substantially less than that calculated for a solid wing subjected to the same heating conditions.
Generalized transport coefficients for inelastic Maxwell mixtures under shear flow.
Garzó, Vicente; Trizac, Emmanuel
2015-11-01
The Boltzmann equation framework for inelastic Maxwell models is considered to determine the transport coefficients associated with the mass, momentum, and heat fluxes of a granular binary mixture in spatially inhomogeneous states close to the simple shear flow. The Boltzmann equation is solved by means of a Chapman-Enskog-type expansion around the (local) shear flow distributions f(r)(0) for each species that retain all the hydrodynamic orders in the shear rate. Due to the anisotropy induced by the shear flow, tensorial quantities are required to describe the transport processes instead of the conventional scalar coefficients. These tensors are given in terms of the solutions of a set of coupled equations, which can be analytically solved as functions of the shear rate a, the coefficients of restitution α(rs), and the parameters of the mixture (masses, diameters, and composition). Since the reference distribution functions f(r)(0) apply for arbitrary values of the shear rate and are not restricted to weak dissipation, the corresponding generalized coefficients turn out to be nonlinear functions of both a and α(rs). The dependence of the relevant elements of the three diffusion tensors on both the shear rate and dissipation is illustrated in the tracer limit case, the results showing that the deviation of the generalized transport coefficients from their forms for vanishing shear rates is in general significant. A comparison with the previous results obtained analytically for inelastic hard spheres by using Grad's moment method is carried out, showing a good agreement over a wide range of values for the coefficients of restitution. Finally, as an application of the theoretical expressions derived here for the transport coefficients, thermal diffusion segregation of an intruder immersed in a granular gas is also studied. PMID:26651684
Generalized transport coefficients for inelastic Maxwell mixtures under shear flow
NASA Astrophysics Data System (ADS)
Garzó, Vicente; Trizac, Emmanuel
2015-11-01
The Boltzmann equation framework for inelastic Maxwell models is considered to determine the transport coefficients associated with the mass, momentum, and heat fluxes of a granular binary mixture in spatially inhomogeneous states close to the simple shear flow. The Boltzmann equation is solved by means of a Chapman-Enskog-type expansion around the (local) shear flow distributions fr(0 ) for each species that retain all the hydrodynamic orders in the shear rate. Due to the anisotropy induced by the shear flow, tensorial quantities are required to describe the transport processes instead of the conventional scalar coefficients. These tensors are given in terms of the solutions of a set of coupled equations, which can be analytically solved as functions of the shear rate a , the coefficients of restitution αr s, and the parameters of the mixture (masses, diameters, and composition). Since the reference distribution functions fr(0 ) apply for arbitrary values of the shear rate and are not restricted to weak dissipation, the corresponding generalized coefficients turn out to be nonlinear functions of both a and αr s. The dependence of the relevant elements of the three diffusion tensors on both the shear rate and dissipation is illustrated in the tracer limit case, the results showing that the deviation of the generalized transport coefficients from their forms for vanishing shear rates is in general significant. A comparison with the previous results obtained analytically for inelastic hard spheres by using Grad's moment method is carried out, showing a good agreement over a wide range of values for the coefficients of restitution. Finally, as an application of the theoretical expressions derived here for the transport coefficients, thermal diffusion segregation of an intruder immersed in a granular gas is also studied.
Inflationary weak anisotropic model with general dissipation coefficient
NASA Astrophysics Data System (ADS)
Sharif, M.; Saleem, Rabia
2016-03-01
This paper explores the dynamics of warm intermediate and logamediate inflationary models during weak dissipative regime with a general form of dissipative coefficient. We analyze these models within the framework of locally rotationally symmetric Bianchi type I universe. In both cases, we evaluate solution of inflaton, effective scalar potential, dissipative coefficient, slow-roll parameters, scalar and tensor power spectra, scalar spectral index and tensor to scalar ratio under slow-roll approximation. We constrain the model parameters using recent data and conclude that anisotropic inflationary universe model with generalized dissipation coefficient remains compatible with WMAP9, Planck and BICEP2 data. Finally, we have checked the effects of bulk viscous pressure on this considered model and found that it remains compatible with recent data only for intermediate case.
NASA Astrophysics Data System (ADS)
Zhou, Jin; Di, Long; Cheng, Changli; Xu, Yuanping; Lin, Zongli
2016-01-01
The stiffness and damping coefficients of active magnetic bearings (AMBs) have direct influence on the dynamic response of a rotor bearing system, including the bending critical speeds, modes of vibrations and stability. Rotor unbalance response is informative in the identification of these bearing support parameters. In this paper, we propose a method for identifying closed-loop AMB stiffness and damping coefficients based on the rotor unbalance response. We will use a flexible rotor-AMB test rig to help describe the proposed method as well as to validate the identification results. First, based on a rigid body model of the rotor, a formula is derived that computes the nominal values of the bearing stiffness and damping coefficients at a given rotating speed from the experimentally measured rotor unbalance response at the given speed. Then, based on a finite element model of the rotor, an error response surface is constructed for each parameter to estimate the identification errors induced by the rotor flexibility. The final identified values of the stiffness and damping coefficients equal the sums of the nominal values initially computed from the unbalance response and the identification errors determined by the error response surfaces. The proposed identification method is carried out on the rotor-AMB test rig. In order to validate the identification results, the identified values of the closed-loop AMB stiffness and damping coefficients are combined with the finite element model of the rotor to form a full model of the rotor-AMB test rig, from which the model unbalance responses at various rotating speeds are determined through simulation and compared with the experimental measurements. The close agreements between the simulation results and the measurements validate the proposed identification method.
Second virial coefficient of a generalized Lennard-Jones potential.
González-Calderón, Alfredo; Rocha-Ichante, Adrián
2015-01-21
We present an exact analytical solution for the second virial coefficient of a generalized Lennard-Jones type of pair potential model. The potential can be reduced to the Lennard-Jones, hard-sphere, and sticky hard-sphere models by tuning the potential parameters corresponding to the width and depth of the well. Thus, the second virial solution can also regain the aforementioned cases. Moreover, the obtained expression strongly resembles the one corresponding to the Kihara potential. In fact, the Fk functions are the same. Furthermore, for these functions, the complete expansions at low and high temperature are given. Additionally, we propose an alternative stickiness parameter based on the obtained second virial coefficient. PMID:25612707
GYutsis: heuristic based calculation of general recoupling coefficients
NASA Astrophysics Data System (ADS)
Van Dyck, D.; Fack, V.
2003-08-01
General angular momentum recoupling coefficients can be expressed as a summation formula over products of 6- j coefficients. Yutsis, Levinson and Vanagas developed graphical techniques for representing the general recoupling coefficient as a cubic graph and they describe a set of reduction rules allowing a stepwise generation of the corresponding summation formula. This paper is a follow up to [Van Dyck and Fack, Comput. Phys. Comm. 151 (2003) 353-368] where we described a heuristic algorithm based on these techniques. In this article we separate the heuristic from the algorithm and describe some new heuristic approaches which can be plugged into the generic algorithm. We show that these new heuristics lead to good results: in many cases we get a more efficient summation formula than our previous approach, in particular for problems of higher order. In addition the new features and the use of our program GYutsis, which implements these techniques, is described both for end users and application programmers. Program summaryTitle of program: CycleCostAlgorithm, GYutsis Catalogue number: ADSA Program Summary URL:http://cpc.cs.qub.ac.uk/summaries/ADSA Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland. Users may obtain the program also by downloading either the compressed tar file gyutsis.tgz (for Unix and Linux) or the zip file gyutsis.zip (for Windows) from our website ( http://caagt.rug.ac.be/yutsis/). An applet version of the program is also available on our website and can be run in a web browser from the URL http://caagt.rug.ac.be/yutsis/GYutsisApplet.html. Licensing provisions: none Computers for which the program is designed: any computer with Sun's Java Runtime Environment 1.4 or higher installed. Programming language used: Java 1.2 (Compiler: Sun's SDK 1.4.0) No. of lines in program: approximately 9400 No. of bytes in distributed program, including test data, etc.: 544 117 Distribution format: tar gzip file Nature of
Bone Strength and Arterial Stiffness Impact on Cardiovascular Mortality in a General Population
Avramovska, Maja; Sikole, Aleksandar
2016-01-01
Osteoporosis and increased arterial stiffness independently have been found to be associated with higher cardiovascular events rates in the general population (GP). We examined 558 patients from GP by dual-energy X-ray absorptiometry (DXA) and pulse wave velocity (PWV) measurements at baseline, with 36-month follow-up period. DXA assessed bone mineral density of femoral neck (BMD FN) and lumbar spine (BMD LS). Carotid-femoral PWV was assessed by pulsed-Doppler. The aim of our study is to find correlation between bone strength and arterial stiffness and their impact on cardiovascular mortality in GP. The mean ± SD of BMD FN, BMD LS, and PWV was 0.852 ± 0.1432 g/cm2, 0.934 ± 0.1546 g/cm2, and 9.209 ± 1.9815 m/s. In multiple regression analysis we found BMD FN (βst = −6.0094, p < 0.0001), hypertension (βst = 1.7340, p < 0.0091), and diabetes (βst = 0.4595, p < 0.0046). With Cox-regression analysis, after 17 cardiovascular events, the significant covariates retained by the backward model were BMD FN (b = −2.4129, p = 0.015) and PWV (b = 0.2606, p = 0.0318). The cut-off values were PWV = 9.4 m/s, BMD FN = 0.783 g/cm2, and BMD LS = 0.992 g/cm2. The results for BMD FN and PWV hazard ratio risk were 1.116 and 1.297, respectively. BMD FN as a measure of bone strength and PWV as a measure of arterial stiffness are strong independent predictors of cardiovascular mortality in GP. PMID:27047700
Bone Strength and Arterial Stiffness Impact on Cardiovascular Mortality in a General Population.
Avramovski, Petar; Avramovska, Maja; Sikole, Aleksandar
2016-01-01
Osteoporosis and increased arterial stiffness independently have been found to be associated with higher cardiovascular events rates in the general population (GP). We examined 558 patients from GP by dual-energy X-ray absorptiometry (DXA) and pulse wave velocity (PWV) measurements at baseline, with 36-month follow-up period. DXA assessed bone mineral density of femoral neck (BMD FN) and lumbar spine (BMD LS). Carotid-femoral PWV was assessed by pulsed-Doppler. The aim of our study is to find correlation between bone strength and arterial stiffness and their impact on cardiovascular mortality in GP. The mean ± SD of BMD FN, BMD LS, and PWV was 0.852 ± 0.1432 g/cm(2), 0.934 ± 0.1546 g/cm(2), and 9.209 ± 1.9815 m/s. In multiple regression analysis we found BMD FN (βst = -6.0094, p < 0.0001), hypertension (βst = 1.7340, p < 0.0091), and diabetes (βst = 0.4595, p < 0.0046). With Cox-regression analysis, after 17 cardiovascular events, the significant covariates retained by the backward model were BMD FN (b = -2.4129, p = 0.015) and PWV (b = 0.2606, p = 0.0318). The cut-off values were PWV = 9.4 m/s, BMD FN = 0.783 g/cm(2), and BMD LS = 0.992 g/cm(2). The results for BMD FN and PWV hazard ratio risk were 1.116 and 1.297, respectively. BMD FN as a measure of bone strength and PWV as a measure of arterial stiffness are strong independent predictors of cardiovascular mortality in GP. PMID:27047700
Abney, Mark
2009-01-01
Summary: Computing the probability of identity by descent sharing among n genes given only the pedigree of those genes is a computationally challenging problem, if n or the pedigree size is large. Here, I present a novel graphical algorithm for efficiently computing all generalized kinship coefficients for n genes. The graphical description transforms the problem from doing many recursion on the pedigree to doing a single traversal of a structure referred to as the kinship graph. Availability: The algorithm is implemented for n = 4 in the software package IdCoefs at http://home.uchicago.edu/abney/Software.html. Contact: abney@bsd.uchicago.edu Supplementary Information:Supplementary data are available at Bioinformatics online. PMID:19359355
Mayer, Otto; Seidlerová, Jitka; Filipovský, Jan; Vágovičová, Petra; Wohlfahrt, Peter; Cífková, Renata; Windrichová, Jindra; Topolčan, Ondřej
2016-04-01
It has been suggested that accumulation of advanced glycation end products (AGEs) is involved in several pathophysiological processes in the vessel wall. We hypothesized that low levels of the soluble receptor for AGEs (sRAGE) might be associated with increased arterial stiffness, a manifestation of vascular ageing in the general population. Using a cross-sectional design, we analyzed 1077 subjects from the Czech post-MONICA study. The aortic pulse wave velocity (aPWV) was measured using a Sphygmocor device. sRAGE concentrations were assessed in frozen samples using enzyme-linked immunosorbent assay methods (R&D Systems). aPWV significantly (P<0.0001) increased across the sRAGE quartiles. An aPWV of 1 m s(-1) was associated with a 37% increase in the risk of low sRAGE (<918 pg ml(-1), bottom quartile; P-value=0.018). In a categorized manner, subjects in the bottom sRAGE quartile had an odds ratio of an increased aPWV (⩾9.3 m s(-1)), adjusted for all potential confounders of 2.05 (95% confidence interval: 1.26-3.32; P=0.004), but this was only the case for non-diabetic hypertensive patients. In contrast, a low sRAGE was rejected as an independent predictor of an increased aPWV in normotensive or diabetic subjects using similar regression models. In conclusion, low circulating sRAGE was independently associated with increased arterial stiffness in a general population-based sample, but this was only observed in hypertensive non-diabetic patients. PMID:26631850
Generalized semiparametric varying-coefficient models for longitudinal data
NASA Astrophysics Data System (ADS)
Qi, Li
In this dissertation, we investigate the generalized semiparametric varying-coefficient models for longitudinal data that can flexibly model three types of covariate effects: time-constant effects, time-varying effects, and covariate-varying effects, i.e., the covariate effects that depend on other possibly time-dependent exposure variables. First, we consider the model that assumes the time-varying effects are unspecified functions of time while the covariate-varying effects are parametric functions of an exposure variable specified up to a finite number of unknown parameters. The estimation procedures are developed using multivariate local linear smoothing and generalized weighted least squares estimation techniques. The asymptotic properties of the proposed estimators are established. The simulation studies show that the proposed methods have satisfactory finite sample performance. ACTG 244 clinical trial of HIV infected patients are applied to examine the effects of antiretroviral treatment switching before and after HIV developing the 215-mutation. Our analysis shows benefit of treatment switching before developing the 215-mutation. The proposed methods are also applied to the STEP study with MITT cases showing that they have broad applications in medical research.
NASA Astrophysics Data System (ADS)
Roedig, C.; Zanotti, O.; Alic, D.
2012-10-01
We present the implementation of an implicit-explicit (IMEX) Runge-Kutta numerical scheme for general relativistic (GR) hydrodynamics coupled to an optically thick radiation field in two existing GR-(magneto)hydrodynamics codes. We argue that the necessity of such an improvement arises naturally in most astrophysically relevant regimes where the optical thickness is high as the equations become stiff. By performing several simple 1D tests, we verify the codes' new ability to deal with this stiffness and show consistency. Then, still in one spatial dimension, we compute a luminosity versus accretion rate diagram for the set-up of spherical accretion on to a Schwarzschild black hole and find good agreement with previous work which included more radiation processes than we currently have available. Lastly, we revisit the supersonic Bondi-Hoyle-Lyttleton (BHL) accretion in two dimensions where we can now present simulations of realistic temperatures, down to T ˜ 106 K or less. Here we find that radiation pressure plays an important role, but also that these highly dynamical set-ups push our approximate treatment towards the limit of physical applicability. The main features of radiation hydrodynamics BHL flows manifest as (i) an effective adiabatic index approaching γeff ˜ 4/3; (ii) accretion rates two orders of magnitude lower than without radiation pressure, but still super-Eddington; (iii) luminosity estimates around the Eddington limit, hence with an overall radiative efficiency as small as ηBHL˜10-2; (iv) strong departures from thermal equilibrium in shocked regions; (v) no appearance of the flip-flop instability. We conclude that the current optically thick approximation to the radiation transfer does give physically substantial improvements over the pure hydro also in set-ups departing from equilibrium, and, once accompanied by an optically thin treatment, is likely to provide a fundamental tool for investigating accretion flows in a large variety of
General dissipation coefficient in low-temperature warm inflation
Bastero-Gil, Mar; Berera, Arjun; Rosa, João G.; Ramos, Rudnei O. E-mail: ab@ph.ed.ac.uk E-mail: joao.rosa@ed.ac.uk
2013-01-01
In generic particle physics models, the inflaton field is coupled to other bosonic and fermionic fields that acquire large masses during inflation and may decay into light degrees of freedom. This leads to dissipative effects that modify the inflationary dynamics and may generate a nearly-thermal radiation bath, such that inflation occurs in a warm rather than supercooled environment. In this work, we perform a numerical computation and obtain expressions for the associated dissipation coefficient in supersymmetric models, focusing on the regime where the radiation temperature is below the heavy mass threshold. The dissipation coefficient receives contributions from the decay of both on-shell and off-shell degrees of freedom, which are dominant for small and large couplings, respectively, taking into account the light field multiplicities. In particular, we find that the contribution from on-shell decays, although Boltzmann-suppressed, can be much larger than that of virtual modes, which is bounded by the validity of a perturbative analysis. This result opens up new possibilities for realizations of warm inflation in supersymmetric field theories.
Ecological optimization and coefficient of performance bounds of general refrigerators
NASA Astrophysics Data System (ADS)
Long, Rui; Liu, Wei
2016-02-01
An analysis of COP and its bounds at maximum ecological criterion for general refrigerators is conducted. For generality, both the non-isothermal heat transfer processes and the internal dissipations are considered. Under different situations, the COP under the maximum ecological criterion have been studied systematically. And the general upper and lower bounds of the optimal COP have been obtained. Furthermore under maximum ecological criterion, the COP of general endoreversible refrigerators have also been studied. And the COP bounds of different kinds of refrigerators have been analyzed. As actual refrigerators may not operate under the condition of maximum COP or maximum cooling load, but operate under the maximum ecological condition which indicates the best compromise between the refrigeration rate and the loss of refrigeration rate. This paper could provide a practical insight for designing and operating actual refrigerators.
Reply to "Comment on `Generalized exclusion processes: Transport coefficients' "
NASA Astrophysics Data System (ADS)
Arita, Chikashi; Krapivsky, P. L.; Mallick, Kirone
2016-07-01
We reply to the Comment of Becker, Nelissen, Cleuren, Partoens, and Van den Broeck [Phys. Rev. E 93, 046101 (2016), 10.1103/PhysRevE.93.046101] on our article [Arita, Krapivsky, and Mallick, Phys. Rev. E 90, 052108 (2014), 10.1103/PhysRevE.90.052108] about the transport properties of a class of generalized exclusion processes.
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.
ERIC Educational Resources Information Center
Henson, Robin K.
In General Linear Model (GLM) analyses, it is important to interpret structure coefficients, along with standardized weights, when evaluating variable contribution to observed effects. Although often used in canonical correlation analysis, structure coefficients are less frequently used in multiple regression and several other multivariate…
Sensitivity of overall vehicle stiffness to local joint stiffness
NASA Technical Reports Server (NTRS)
Chon, Choon T.
1987-01-01
How overall vehicle stiffness is affected by local joint stiffness is discussed. By using the principle of virtual work and the minimum strain energy theorem, a closed form expression for the sensitivity coefficient was derived. The insensitivity of the vehicle stiffness to a particular joint, when its stiffness exceeds a certain value (or threshold value), was proven mathematically. In order to investigate the sensitivity of the structure to the joint stiffness, a so-called stick model was created, and the modeling technique is briefly described. Some data on joint stiffness of tested vehicles are also presented.
NASA Astrophysics Data System (ADS)
Contarino, Christian; Toro, Eleuterio F.; Montecinos, Gino I.; Borsche, Raul; Kall, Jochen
2016-06-01
In this paper we design a new implicit solver for the Junction-Generalized Riemann Problem (J-GRP), which is based on a recently proposed implicit method for solving the Generalized Riemann Problem (GRP) for systems of hyperbolic balance laws. We use the new J-GRP solver to construct an ADER scheme that is globally explicit, locally implicit and with no theoretical accuracy barrier, in both space and time. The resulting ADER scheme is able to deal with stiff source terms and can be applied to non-linear systems of hyperbolic balance laws in domains consisting on networks of one-dimensional sub-domains. In this paper we specifically apply the numerical techniques to networks of blood vessels. We report on a test problem with exact solution for a simplified network of three vessels meeting at a single junction, which is then used to carry out a systematic convergence rate study of the proposed high-order numerical methods. Schemes up to fifth order of accuracy in space and time are implemented and tested. We then show the ability of the ADER scheme to deal with stiff sources through a numerical simulation in a network of vessels. An application to a physical test problem consisting of a network of 37 compliant silicon tubes (arteries) and 21 junctions, reveals that it is imperative to use high-order methods at junctions, in order to preserve the desired high order of accuracy in the full computational domain. For example, it is demonstrated that a second-order method throughout, gives comparable results to a method that is fourth order in the interior of the domain and first order at junctions.
Generalized skew coefficient for flood frequency computations for the State of Hawaii
Lee, Reuben
1984-01-01
In 1976, the Hydrology Committee of the U.S. Water Resources Council estimated a generalized skew coefficient for flood frequency computations of -0.05 for the State of Hawaii. This value is the average of 30 stream gaging stations with 25 or more years of record through water year 1973. This report updates the generalized skew coefficient for the State of Hawaii to -0.14. It is the average of 68 stream gaging stations with 25 or more years of record. (USGS)
NASA Technical Reports Server (NTRS)
Bert, C. W.; Chang, S.
1972-01-01
Elastic and damping analyses resulting in determinations of the various stiffnesses and associated loss tangents for the complete characterization of the elastic and damping behavior of a monofilament composite layer are presented. For the determination of the various stiffnesses, either an elementary mechanics-of-materials formulation or a more rigorous mixed-boundary-value elasticity formulation is used. The solution for the latter formulation is obtained by means of the boundary-point least-square error technique. Kimball-Lovell type damping is assumed for each of the constituent materials. For determining the loss tangents associated with the various stiffnesses, either the viscoelastic correspondence principle or an energy analysis based on the appropriate elastic stress distribution is used.
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…
NASA Astrophysics Data System (ADS)
Zayed, Elsayed M. E.; Abdelaziz, Mahmoud A. M.
2010-09-01
In this article, the generalized G'/G-expansion method using a generalized wave transformation is applied to find exact traveling wave solutions of the generalized Zakharov-Kuznetsov equation with variable coefficients. As a result, hyperbolic, trigonometric and rational function solutions with parameters are obtained. When these parameters are taken special values, the solitary wave solutions are derived from the hyperbolic function solution. It is shown that the proposed method is direct, effective and can be applied to many other nonlinear evolution equations in mathematical physics.
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 χ 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 χ 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.
Neoclassical transport coefficients for general axisymmetric equilibria in the banana regime
NASA Astrophysics Data System (ADS)
Angioni, C.; Sauter, O.
2000-04-01
Using the standard approach of neoclassical theory, a set of relatively simple kinetic equations has been obtained, suited for an implementation in a numerical code to compute a related set of distribution functions. The transport coefficients are then expressed by simple integrals of these functions and they can be easily computed numerically. The code CQL3D [R. W. Harvey and M. G. McCoy, in Proceedings of IAEA Technical Committee Meeting on Advances in Simulation and Modeling of Thermonuclear Plasmas, Montreal, 1992 (International Atomic Energy Agency, Vienna, 1993), pp. 489-526], which uses the full collision operator and considers the realistic axisymmetric configuration of the magnetic surfaces, has been modified to solve the bounce-averaged version of these equations. The coefficients have then been computed for a wide variety of equilibrium parameters, high-lighting interesting features of the influence of geometry at small aspect ratio. Differences with the most recent formulas for the ion neoclassical heat conductivity are pointed out. A set of formulas, which fit the code results, is obtained to easily evaluate all the neoclassical transport coefficients in the banana regime, at all aspect ratios, in general axisymmetric equilibria. This work extends to all the other transport coefficients, at least in the banana regime, the work of Sauter et al. [O. Sauter, C. Angioni, and Y. R. Lin-Liu, Phys. Plasmas 6, 2834 (1999)] which evaluates the neoclassical conductivity and all the bootstrap current coefficients. Formulas for arbitrary collisionality regime are proposed, obtained combining our results for the banana regime with the results of Hinton and Hazeltine [F. L. Hinton and R. D. Hazeltine, Rev. Mod. Phys. 48, 239 (1976)], adapted for small aspect ratio.
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.
Sugama, H.; Nishimura, S.
2008-04-15
A detailed comparison is made between moment-equation methods presented by H. Sugama and S. Nishimura [Phys. Plasmas 9, 4637 (2002)] and by M. Taguchi [Phys. Fluids B 4, 3638 (1992)] for calculating neoclassical transport coefficients in general toroidal plasmas including nonsymmetric systems. It is shown that these methods can be derived from the drift kinetic equation with the same collision model used for correctly taking account of collisional momentum conservation. In both methods, the Laguerre polynomials of the energy variable are employed to expand the guiding-center distribution function and to obtain the moment equations, by which the radial neoclassical transport fluxes and the parallel flows are related to the thermodynamic forces. The methods are given here in the forms applicable for an arbitrary truncation number of the Laguerre-polynomial expansion so that their accuracies can be improved by increasing the truncation number. Differences between results from the two methods appear when the Laguerre-polynomial expansion is truncated up to a finite order because different weight functions are used in them to derive the moment equations. At each order of the truncation, the neoclassical transport coefficients obtained from the Sugama-Nishimura method show the Onsager symmetry and satisfy the ambipolar-diffusion condition intrinsically for symmetric systems. Also, numerical examples are given to show how the transport coefficients converge with the truncation number increased for the two methods.
NASA Astrophysics Data System (ADS)
Tatsii, R. M.; Pazen, O. Yu.
2016-03-01
A constructive scheme for the construction of a solution of a mixed problem for the heat conduction equation with piecewise-continuous coefficients coordinate-dependent in the final interval is suggested and validated in the present work. The boundary conditions are assumed to be most general. The scheme is based on: the reduction method, the concept of quasi-derivatives, the currently accepted theory of the systems of linear differential equations, the Fourier method, and the modified method of eigenfunctions. The method based on this scheme should be related to direct exact methods of solving mixed problems that do not employ the procedures of constructing Green's functions or integral transformations. Here the theorem of eigenfunction expansion is adapted for the case of coefficients that have discontinuity points of the 1st kind. The results obtained can be used, for example, in investigating the process of heat transfer in a multilayer slab under conditions of ideal thermal contact between the layers. A particular case of piecewise-continuous coefficients is considered. A numerical example of calculation of a temperature field in a real four-layer building slab under boundary conditions of the 3rd kind (conditions of convective heat transfer) that model the phenomenon of fire near one of the external surfaces is given.
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.
Oosterhoff, Thijs C H; Nota, Sjoerd P F T; Ring, David
2015-06-01
Background Finger stiffness varies substantially in patients with hand and upper extremity illness and can be notably more than expected for a given pathophysiology. In prior studies, pain intensity and magnitude of disability consistently correlate with coping strategies such as catastrophic thinking and kinesiophobia, which can be characterized as overprotectiveness. In this retrospective study we address the primary research question whether patients with finger stiffness are more often overprotective when the primary pathology is outside the hand (e.g. distal radius fracture) than when it is located within the hand. Methods In an orthopaedic hand surgery department 160 patients diagnosed with more finger stiffness than expected for a given pathophysiology or time point of recovery between December 2006 and September 2012 were analyzed to compare the proportion of patients characterized as overprotective for differences by site of pathology: (1) inside the hand, (2) outside the hand, and (3) psychiatric etiology (e.g. clenched fist). Results Among 160 subjects with more finger stiffness than expected, 132 (82 %) were characterized as overprotective including 88 of 108 (81 %) with pathology in the hand, 39 of 44 (89 %) with pathology outside the hand, and 5 of 8 (63 %) with psychiatric etiology. These differences were not significant. Conclusions Overprotectiveness is common in patients with more finger stiffness than expected regardless the site and type of primary pathology. It seems worthwhile to recognize and treat maladaptive coping strategies early during recovery to limit impairment, symptoms, and disability. PMID:26078497
Lü, Xing; Tian, Bo; Zhang, Hai-Qiang; Xu, Tao; Li, He
2010-12-01
Gardner model describes certain nonlinear elastic structures, ion-acoustic waves in plasmas, and shear flows in ocean and atmosphere. In this paper, by virtue of the computerized symbolic computation, the integrability of a generalized (2+1)-dimensional variable-coefficient Gardner model is investigated. Painlevé integrability conditions are derived among the coefficient functions, which reduce all the coefficient functions to be proportional only to γ(t), the coefficient of the cubic nonlinear term u(2)u(x). Then, an independent transformation of the variable t transforms the reduced γ(t)-dependent equation into a constant-coefficient integrable one. Painlevé test shows that this is the only case when our original generalized (2+1)-dimensional variable-coefficient Gardner model is integrable. PMID:21198095
NASA Technical Reports Server (NTRS)
Ray, Sujit K.; Utku, Senol; Wada, Ben K.
1986-01-01
The stiffness-matrix formulation for the rectangular finite element described by Melosh (1963) and Weaver and Johnston (1984) is generalized to orthotropic materials with material axes not necessarily coincident with the x and y axes; i.e., the condition d(13) = d(23) = 0 is removed. Also included are explicit expressions for the element load vector associated with nonuniform temperature increase in the element. Applications to the analysis of thermal stresses in thin Si-crystal ribbons subjected to temperature changes with highly nonuniform lengthwise and transverse gradients (Utku et al., 1986) and to the simulation of the thermoviscoelastic behavior of growing Si ribbons (Utku and Ray, 1986) are indicated.
Elnaggar, Sameh Y.; Tervo, Richard J.; Mattar, Saba M.
2015-11-21
The theory and operation of various devices and systems, such as wireless power transfer via magnetic resonant coupling, magneto-inductive wave devices, magnetic resonance spectroscopy probes, and metamaterials can rely on coupled tuned resonators. The coupling strength is usually expressed in terms of the coupling coefficient κ, which can have electrical κ{sub E} and/or magnetic κ{sub M} components. In the current article, general expressions of κ are derived. The relation between the complex Poynting equation in its microscopic form and κ is made and discussed in detail. It is shown that κ can be expressed in terms of the interaction energy between the resonators' modes. It thus provides a general form that combines the magnetic and electric components of κ. The expressions make it possible to estimate the frequencies and fields of the coupled modes for arbitrarily oriented and spaced resonators. Thus, enabling the calculation of system specific parameters such as the transfer efficiency of wireless power transfer systems, resonator efficiency for electron spin resonance probes, and dispersion relations of magneto-inductive and stereo-metamaterials structures.
NASA Astrophysics Data System (ADS)
Elnaggar, Sameh Y.; Tervo, Richard J.; Mattar, Saba M.
2015-11-01
The theory and operation of various devices and systems, such as wireless power transfer via magnetic resonant coupling, magneto-inductive wave devices, magnetic resonance spectroscopy probes, and metamaterials can rely on coupled tuned resonators. The coupling strength is usually expressed in terms of the coupling coefficient κ, which can have electrical κE and/or magnetic κM components. In the current article, general expressions of κ are derived. The relation between the complex Poynting equation in its microscopic form and κ is made and discussed in detail. It is shown that κ can be expressed in terms of the interaction energy between the resonators' modes. It thus provides a general form that combines the magnetic and electric components of κ. The expressions make it possible to estimate the frequencies and fields of the coupled modes for arbitrarily oriented and spaced resonators. Thus, enabling the calculation of system specific parameters such as the transfer efficiency of wireless power transfer systems, resonator efficiency for electron spin resonance probes, and dispersion relations of magneto-inductive and stereo-metamaterials structures.
A general correlation to predict axial dispersion coefficients in aerated channel reactors.
Lemoullec, Yann; Potier, Olivier; Gentric, Caroline; Leclerc, Jean-Pierre
2008-03-01
Tracer studies have been widely applied to characterize the flow behavior in activated sludge reactors. The channel reactor with bottom aerators is one of the widespread designs in large wastewater treatment plants. Its flow behavior is well modeled either as a plug flow reactor with axial dispersion or as the perfect mixing cells in series. Several correlations have been developed to estimate the dispersion coefficients as a function of operating and geometrical parameters. These correlations fit properly the data derived from a given reactor in the range of operating and geometrical parameters for which they have been determined. Unfortunately they cannot be applied straightforwardly with a sufficient level of confidence to scale-up industrial units or scale-down laboratory pilots. Recently, two papers have proposed more general correlations [Makinia, J., Wells, S.A., 2005. Evaluation of empirical formulae for estimation of the longitudinal dispersion in activated sludge reactors. Water Res. 39, 1533-1542; Potier, O., Leclerc, J.-P., Pons, M.-N., 2005. Influence of geometrical and operating parameters on the axial dispersion in an aerated channel reactor. Water Res. 39, 4454-4462] but they are still not able to represent the whole set of data from the literature. This paper proposes a general correlation, which can represent all the available and usable sets of data from the literature and more than 170 experimental results obtained in our laboratory with a precision of 18%. PMID:18063006
Stiffness characteristics of longwall shields
Bayczak, T.M.; Schwemmer, D.E.
1988-01-01
The stiffness characteristics of longwall shields have been investigated the this study. Since longwall strata activity is characterized by roof-to-floor and face-to-waste displacements, a model with two degrees of freedom is used to describe the load-displacement relationship of the shield structure. The model considers the support as an elastic body and relates horizontal and vertical resultant forces acting on the support to associated displacements as a function of the stiffness of the support structure. Stiffness coefficients under full canopy and base contact configurations have been determined.
A computer program for two-particle generalized coefficients of fractional parentage
NASA Astrophysics Data System (ADS)
Deveikis, A.; Juodagalvis, A.
2008-10-01
We present a FORTRAN90 program GCFP for the calculation of the generalized coefficients of fractional parentage (generalized CFPs or GCFP). The approach is based on the observation that the multi-shell CFPs can be expressed in terms of single-shell CFPs, while the latter can be readily calculated employing a simple enumeration scheme of antisymmetric A-particle states and an efficient method of construction of the idempotent matrix eigenvectors. The program provides fast calculation of GCFPs for a given particle number and produces results possessing numerical uncertainties below the desired tolerance. A single j-shell is defined by four quantum numbers, (e,l,j,t). A supplemental C++ program parGCFP allows calculation to be done in batches and/or in parallel. Program summaryProgram title:GCFP, parGCFP Catalogue identifier: AEBI_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBI_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 17 199 No. of bytes in distributed program, including test data, etc.: 88 658 Distribution format: tar.gz Programming language: FORTRAN 77/90 ( GCFP), C++ ( parGCFP) Computer: Any computer with suitable compilers. The program GCFP requires a FORTRAN 77/90 compiler. The auxiliary program parGCFP requires GNU-C++ compatible compiler, while its parallel version additionally requires MPI-1 standard libraries Operating system: Linux (Ubuntu, Scientific) (all programs), also checked on Windows XP ( GCFP, serial version of parGCFP) RAM: The memory demand depends on the computation and output mode. If this mode is not 4, the program GCFP demands the following amounts of memory on a computer with Linux operating system. It requires around 2 MB of RAM for the A=12 system at E⩽2. Computation of the A=50 particle system requires around 60 MB of
NASA Astrophysics Data System (ADS)
Ryu, Ji-Woo; Lee, Seon-Oh; Sim, Dong-Gyu; Han, Jong-Ki
2012-02-01
We present a no-reference peak signal to noise ratio (PSNR) estimation algorithm based on discrete cosine transform (DCT) coefficient distributions from H.264/MPEG-4 part 10 advanced video codec (H.264/AVC) bitstreams. To estimate the PSNR of a compressed picture without the original picture on the decoder side, it is important to model the distribution of transform coefficients obtained from quantized coefficients accurately. Whereas several conventional algorithms use the Laplacian or Cauchy distribution to model the DCT coefficient distribution, the proposed algorithm uses a generalized Gaussian distribution. Pearson's χ2 (chi-square) test was applied to show that the generalized Gaussian distribution is more appropriate than the other models for modeling the transform coefficients. The χ2 test was also used to find optimum parameters for the generalized Gaussian model. It was found that the generalized Gaussian model improves the accuracy of the DCT coefficient distribution, thus reducing the mean squared error between the real and the estimated PSNR.
Yu, Xin; Gao, Yi-Tian; Sun, Zhi-Yuan; Liu, Ying
2011-05-01
Under investigation is a generalized variable-coefficient forced Korteweg-de Vries equation in fluids and other fields. From the bilinear form of such equation, the N-soliton solution and a type of analytic solution are constructed with symbolic computation. Analytic analysis indicates that: (1) dispersive and dissipative coefficients affect the solitonic velocity; (2) external-force term affects the solitonic velocity and background; (3) line-damping coefficient and some parameters affect the solitonic velocity, background, and amplitude. Solitonic propagation and interaction can be regarded as the combination of the effects of various variable coefficients. According to a constraint among the nonlinear, dispersive, and line-damping coefficients in this paper, the possible applications of our results in the real world are also discussed in three aspects, i.e., solution with the constraint, solution without the constraint, and approximate solution. PMID:21728676
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.
Satomura, Hironori; Adachi, Kohei
2013-07-01
To facilitate the interpretation of canonical correlation analysis (CCA) solutions, procedures have been proposed in which CCA solutions are orthogonally rotated to a simple structure. In this paper, we consider oblique rotation for CCA to provide solutions that are much easier to interpret, though only orthogonal rotation is allowed in the existing formulations of CCA. Our task is thus to reformulate CCA so that its solutions have the freedom of oblique rotation. Such a task can be achieved using Yanai's (Jpn. J. Behaviormetrics 1:46-54, 1974; J. Jpn. Stat. Soc. 11:43-53, 1981) generalized coefficient of determination for the objective function to be maximized in CCA. The resulting solutions are proved to include the existing orthogonal ones as special cases and to be rotated obliquely without affecting the objective function value, where ten Berge's (Psychometrika 48:519-523, 1983) theorems on suborthonormal matrices are used. A real data example demonstrates that the proposed oblique rotation can provide simple, easily interpreted CCA solutions. PMID:25106398
Shu, Huazhong; Luo, Limin; Han, Guo-Niu; Coatrieux, Jean-Louis
2006-01-01
Zernike polynomials have been widely used to describe the aberrations in wave-front sensing of the eye. The Zernike coefficients are often computed under different aperture sizes. For the sake of comparison, the same aperture diameter is required. Since no standard aperture size is available for reporting the results, it is important to develop a technique for converting the Zernike coefficients obtained from one aperture size to another size. In this paper, by investigating the properties of Zernike polynomials, we propose a general method for establishing the relationship between two sets of Zernike coefficients computed with different aperture sizes. PMID:16835654
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…
Avolio, Alberto
2013-01-01
Stiffness of large arteries has been long recognized as a significant determinant of pulse pressure. However, it is only in recent decades, with the accumulation of longitudinal data from large and varied epidemiological studies of morbidity and mortality associated with cardiovascular disease, that it has emerged as an independent predictor of cardiovascular risk. This has generated substantial interest in investigations related to intrinsic causative and associated factors responsible for the alteration of mechanical properties of the arterial wall, with the aim to uncover specific pathways that could be interrogated to prevent or reverse arterial stiffening. Much has been written on the haemodynamic relevance of arterial stiffness in terms of the quantification of pulsatile relationships of blood pressure and flow in conduit arteries. Indeed, much of this early work regarded blood vessels as passive elastic conduits, with the endothelial layer considered as an inactive lining of the lumen and as an interface to flowing blood. However, recent advances in molecular biology and increased technological sophistication for the detection of low concentrations of biochemical compounds have elucidated the highly important regulatory role of the endothelial cell affecting vascular function. These techniques have enabled research into the interaction of the underlying passive mechanical properties of the arterial wall with the active cellular and molecular processes that regulate the local environment of the load-bearing components. This review addresses these emerging concepts. PMID:26587425
Stiffness characteristics of longwall shields
Barczak, T.M.; Schwemmer, D.E.
1988-01-01
Since longwall strata activity is characterized by roof-to-floor and face-to-waste displacements, a model with two degrees of freedom was used to describe the load-displacement relationship of the shield structure. The model considers the support as an elastic body and relates horizontal and vertical resultant forces acting on the support to associated displacements as a function of the stiffness of the support structure. Stiffness coefficients under full canopy and base contact configurations were determined by controlled displacement loading of longwall shields in the Bureau's Mine Roof Simulator. These two-legged longwall shields of different manufacture were investigated. The stiffness characteristics of these shields were evaluated relative to two parameters, namely, shield height and setting pressure. The tests results indicate a reduction in shield stiffness for increasing height. Setting pressure was found to have less of an effect on shield stiffness, producing only a slight increase in stiffness as setting pressure increased. Similar trends were observed for all three shields, indicating a similarity in stiffness characteristics for shields of the same basic configuration.
Hadavi, Shahrzad; Noyce, Alastair J; Leslie, R David; Giovannoni, Gavin
2011-10-01
Stiff person syndrome (SPS) is a rare disorder, characterised by fluctuating rigidity and stiffness of the axial and proximal lower limb muscles, with superimposed painful spasms and continuous motor unit activity on electromyography. Although rare in general neurology practice, once observed it is unforgettable. The general neurologist may see only one or two cases during his or her career and as such it remains underdiagnosed. Left untreated, SPS symptoms can progress to cause significant disability. Patients have a poor quality of life and an excess rate of comorbidity and mortality. The severity of symptoms and lack of public awareness of the condition create anxiety and uncertainty for people with the disease. This review aims to raise awareness of SPS and to improve the likelihood of its earlier diagnosis and treatment. PMID:21921002
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.
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.
NASA Astrophysics Data System (ADS)
Herrera, Ramón; Olivares, Marco; Videla, Nelson
2014-09-01
In this paper, we study a warm intermediate inflationary model with a general form for the dissipative coefficient Γ(T, ϕ) = CϕTm/ϕm-1 in the context of Loop Quantum Cosmology (LQC). We examine this model in the weak and strong dissipative regimes. In general, we discuss in great detail the characteristics of this model in the slow-roll approximation. Also, we assume that the modifications to perturbation equations result exclusively from Hubble rate. In this approach, we use recent astronomical observations from Planck and BICEP2 experiments to restrict the parameters in our model.
Stability domains of the delay and PID coefficients for general time-delay systems
NASA Astrophysics Data System (ADS)
Almodaresi, Elham; Bozorg, Mohammad; Taghirad, Hamid D.
2016-04-01
Time delays are encountered in many physical systems, and they usually threaten the stability and performance of closed-loop systems. The problem of determining all stabilising proportional-integral-derivative (PID) controllers for systems with perturbed delays is less investigated in the literature. In this study, the Rekasius substitution is employed to transform the system parameters to a new space. Then, the singular frequency (SF) method is revised for the Rekasius transformed system. A novel technique is presented to compute the ranges of time delay for which stable PID controller exists. This stability range cannot be readily computed from the previous methods. Finally, it is shown that similar to the original SF method, finite numbers of singular frequencies are sufficient to compute the stable regions in the space of time delay and controller coefficients.
Coefficient of performance and its bounds for general refrigerators with nonisothermal processes
NASA Astrophysics Data System (ADS)
Long, Rui; Liu, Wei
2014-08-01
An analysis of the coefficient of performance (COP) and its bounds at maximum \\chi figure of merit for refrigerators is conducted and the heat transfer processes are described using Newton’s law of cooling with a time-dependent heat conductance. The upper bound of the COP, {{\\varepsilon }_{CA}}=\\sqrt{{{\\varepsilon }_{C}}+1}-1, is independent of the time duration completing either process or the heat conductance. The optimal temperature profiles in the heat exchanging processes are analyzed under different dimensionless contact time limits. Provided the dimensionless contact times satisfy certain relations, the endoreversible model is recovered. Furthermore, numerical calculations are conducted to investigate the effect of different heat conductances on temperature profiles under the maximum \\chi criterion. This work can guide design and operation of actual refrigerators.
ERIC Educational Resources Information Center
Vacha-Haase, Tammi; Kogan, Lori R.; Tani, Crystal R.; Woodall, Renee A.
2001-01-01
Used reliability generalization to explore the variance of scores on 10 Minnesota Multiphasic Personality Inventory (MMPI) clinical scales drawing on 1,972 articles in the literature on the MMPI. Results highlight the premise that scores, not tests, are reliable or unreliable, and they show that study characteristics do influence scores on the…
NASA Astrophysics Data System (ADS)
Wang, Lu; Wu, Li-Wei; Wei, Le; Gao, Juan; Sun, Cui-Li; Chai, Pei; Li, Dao-Wu
2014-02-01
The accuracy of attenuation correction in positron emission tomography scanners depends mainly on deriving the reliable 511-keV linear attenuation coefficient distribution in the scanned objects. In the PET/CT system, the linear attenuation distribution is usually obtained from the intensities of the CT image. However, the intensities of the CT image relate to the attenuation of photons in an energy range of 40 keV-140 keV. Before implementing PET attenuation correction, the intensities of CT images must be transformed into the PET 511-keV linear attenuation coefficients. However, the CT scan parameters can affect the effective energy of CT X-ray photons and thus affect the intensities of the CT image. Therefore, for PET/CT attenuation correction, it is crucial to determine the conversion curve with a given set of CT scan parameters and convert the CT image into a PET linear attenuation coefficient distribution. A generalized method is proposed for converting a CT image into a PET linear attenuation coefficient distribution. Instead of some parameter-dependent phantom calibration experiments, the conversion curve is calculated directly by employing the consistency conditions to yield the most consistent attenuation map with the measured PET data. The method is evaluated with phantom experiments and small animal experiments. In phantom studies, the estimated conversion curve fits the true attenuation coefficients accurately, and accurate PET attenuation maps are obtained by the estimated conversion curves and provide nearly the same correction results as the true attenuation map. In small animal studies, a more complicated attenuation distribution of the mouse is obtained successfully to remove the attenuation artifact and improve the PET image contrast efficiently.
Rotordynamic coefficient test results for a four-stage brush seal
NASA Astrophysics Data System (ADS)
Conner, Kelly J.; Childs, Dara W.
1993-06-01
Experimental results are presented for the direct and cross-coupled stiffness and direct damping coefficients for a four-stage brush seal. Variable test parameters include the inlet pressure, pressure ratio, shaft speed, fluid prerotation, and seal spacing. Direct damping slightly increases with running speed; otherwise, the rotordynamic coefficients are relatively insensitive to changes in the test parameters. Cross-coupled stiffness is generally unchanged by increasing the inlet tangential velocity to the seals, in contrast to conventional labyrinth seals. Comparisons of test results for the four-stage brush seal with an eight-cavity labyrinth showed superior rotordynamic performance for the brush seal, namely, larger values for direct stiffness and lower values for the (destabilizing) cross-coupled stiffness coefficient.
Dimitriadis, Alexandros I.; Kantartzis, Nikolaos V.; Tsiboukis, Theodoros D.; Hafner, Christian
2015-01-15
Highlights: •Formulas for E/M fields radiated by continuous surface polarization distributions. •Non-local effective surface susceptibility model for periodic metafilms. •Generalized reflection and transmission coefficients for an arbitrary metafilm. •Successful treatment of non-planar scatterer arrays and spatial dispersion effects. -- Abstract: A non-local surface susceptibility model for the consistent description of periodic metafilms formed by arbitrarily-shaped, electrically-small, bianisotropic scatterers is developed in this paper. The rigorous scheme is based on the point-dipole approximation technique and is valid for any polarization and propagation direction of an electromagnetic wave impinging upon the metafilm, unlike existing approaches whose applicability is practically confined to very specific cases of incidence. Next, the universal form of the resulting surface susceptibility matrix is employed for the derivation of the generalized Fresnel coefficients for such surfaces, which enable the comprehensive interpretation of several significant, yet relatively unexamined, physical interactions. Essentially, these coefficients include eight distinct terms, corresponding to the co-polarized and cross-polarized reflection and transmission coefficients for the two orthogonal eigenpolarizations of a linearly-polarized incident plane wave. The above formulas are, then, utilized for the prediction of the scattering properties of metafilms with different planar and non-planar resonators, which are characterized via the featured model and two previously reported local ones. Their comparison with numerical simulation outcomes substantiates the merits of the proposed method, reveals important aspects of the underlying physics, and highlights the differences between the various modeling procedures.
Generalized Skew Coefficients of Annual Peak Flows for Rural, Unregulated Streams in West Virginia
Atkins, John T.; Wiley, Jeffrey B.; Paybins, Katherine S.
2009-01-01
Generalized skew was determined from analysis of records from 147 streamflow-gaging stations in or near West Virginia. The analysis followed guidelines established by the Interagency Advisory Committee on Water Data described in Bulletin 17B, except that stations having 50 or more years of record were used instead of stations with the less restrictive recommendation of 25 or more years of record. The generalized-skew analysis included contouring, averaging, and regression of station skews. The best method was considered the one with the smallest mean square error (MSE). MSE is defined as the following quantity summed and divided by the number of peaks: the square of the difference of an individual logarithm (base 10) of peak flow less the mean of all individual logarithms of peak flow. Contouring of station skews was the best method for determining generalized skew for West Virginia, with a MSE of about 0.2174. This MSE is an improvement over the MSE of about 0.3025 for the national map presented in Bulletin 17B.
Geng, S; Lei, X; Toyohara, J P; Zhan, P; Wang, J; Tan, S
2006-07-01
Stiff skin syndrome is a rare disorder characterized by pronounced skin induration, mild hypertrichosis and limited joint mobility, predominantly on the buttocks and thighs. Many heterogeneous cases have been reported under the name of stiff skin syndrome. We present a case of stiff skin syndrome from China, the diagnosis based on the patient's typical clinical and histopathological features. PMID:16836505
Estes, Jason P.; Nguyen, Danh V.; Dalrymple, Lorien S.; Mu, Yi; Şentürk, Damla
2014-01-01
Among patients on dialysis, cardiovascular disease and infection are leading causes of hospitalization and death. Although recent studies have found that the risk of cardiovascular events is higher after an infection-related hospitalization, studies have not fully elucidated how the risk of cardiovascular events changes over time for patients on dialysis. In this work, we characterize the dynamics of cardiovascular event risk trajectories for patients on dialysis while conditioning on survival status via multiple time indices: (1) time since the start of dialysis, (2) time since the pivotal initial infection-related hospitalization and (3) the patient’s age at the start of dialysis. This is achieved by using a new class of generalized multiple-index varying coefficient (GM-IVC) models. The proposed GM-IVC models utilize a multiplicative structure and one-dimensional varying coefficient functions along each time and age index to capture the cardiovascular risk dynamics before and after the initial infection-related hospitalization among the dynamic cohort of survivors. We develop a two-step estimation procedure for the GM-IVC models based on local maximum likelihood. We report new insights on the dynamics of cardiovascular events risk using the United States Renal Data System database, which collects data on nearly all patients with end-stage renal disease in the U.S. Finally, simulation studies assess the performance of the proposed estimation procedures. PMID:24766178
NASA Technical Reports Server (NTRS)
Coward, Adrian V.; Papageorgiou, Demetrios T.; Smyrlis, Yiorgos S.
1994-01-01
In this paper the nonlinear stability of two-phase core-annular flow in a pipe is examined when the acting pressure gradient is modulated by time harmonic oscillations and viscosity stratification and interfacial tension is present. An exact solution of the Navier-Stokes equations is used as the background state to develop an asymptotic theory valid for thin annular layers, which leads to a novel nonlinear evolution describing the spatio-temporal evolution of the interface. The evolution equation is an extension of the equation found for constant pressure gradients and generalizes the Kuramoto-Sivashinsky equation with dispersive effects found by Papageorgiou, Maldarelli & Rumschitzki, Phys. Fluids A 2(3), 1990, pp. 340-352, to a similar system with time periodic coefficients. The distinct regimes of slow and moderate flow are considered and the corresponding evolution is derived. Certain solutions are described analytically in the neighborhood of the first bifurcation point by use of multiple scales asymptotics. Extensive numerical experiments, using dynamical systems ideas, are carried out in order to evaluate the effect of the oscillatory pressure gradient on the solutions in the presence of a constant pressure gradient.
NASA Technical Reports Server (NTRS)
Nelson, C. C.; Childs, D. W.; Nicks, C.; Elrod, D.
1985-01-01
The leakage and rotordynamic coefficients of constant-clearance and convergent-tapered annular gas seals were measured in an experimental test facility. The results are presented along with the theoretically predicted values. Of particular interest is the prediction that optimally tapered seals have significantly larger direct stiffness than straight seals. The experimental results verify this prediction. Generally the theory does quite well, but fails to predict the large increase in direct stiffness when the fluid is pre-rotated.
Lumia, Richard; Baevsky, Yvonne H.
2000-01-01
Flood-frequency relations that are developed by fitting the logarithms of annual peak discharges to a Pearson Type-III distribution are sensitive to skew coefficients. Estimates of population skew for a site are improved when computed from the weighted average of (1) the sample (station) skew, and (2) an unbiased, generalized skew estimate. A weighting technique based on the number of years of record at each of 226 sites was used to develop a contour map of unbiased, generalized skew coefficients for New York. An attempt was made to group (regionalize) the station skew coefficients into five hydrologically similar areas of New York, but the statewide version proved to be as accurate as the regionalized version and therefore was adopted as the final generalized skew-coefficient map for New York. An error analysis showed the statewide contour map to have lower MSE?s (mean square errors) than those computed from (1) the five regional skewcoefficient contour maps, (2) a previously used (1982) nationwide skew coefficient map, and (3) the weighted mean of skew coefficients for sites within each of five hydrologically uniform, but distinct areas of New York.
Optimized stiffness for linear time-invariant dynamic system according to a new system design
NASA Astrophysics Data System (ADS)
Veeraklaew, Tawiwat
2012-11-01
This paper deals with a linear time-invariant dynamic system such as spring-mass-damper system. General dynamic systems are quite commonly to be redesigned for another purpose of using. For example, if one automobile must be redesigned to have more weights, the existing suspension must be replaced due to that gained weight. Therefore the stiffness and damping coefficient must be recomputed in order to make the automobile become suitable for using as previous. Here the spring-mass-damper system is used as an example to demonstrate the technique through dynamic optimization where the problem is solved in two categories as minimum energy and maximum jerk. Once the state and control variables are provided from the problem of minimum energy and maximum jerk, respectively, these parameter will be substituted in dynamic equations and leave the stiffness and damping coefficient as the unknown parameters to be solved.
Hierarchies of plant stiffness.
Brulé, Veronique; Rafsanjani, Ahmad; Pasini, Damiano; Western, Tamara L
2016-09-01
Plants must meet mechanical as well as physiological and reproductive requirements for survival. Management of internal and external stresses is achieved through their unique hierarchical architecture. Stiffness is determined by a combination of morphological (geometrical) and compositional variables that vary across multiple length scales ranging from the whole plant to organ, tissue, cell and cell wall levels. These parameters include, among others, organ diameter, tissue organization, cell size, density and turgor pressure, and the thickness and composition of cell walls. These structural parameters and their consequences on plant stiffness are reviewed in the context of work on stems of the genetic reference plant Arabidopsis thaliana (Arabidopsis), and the suitability of Arabidopsis as a model system for consistent investigation of factors controlling plant stiffness is put forward. Moving beyond Arabidopsis, the presence of morphological parameters causing stiffness gradients across length-scales leads to beneficial emergent properties such as increased load-bearing capacity and reversible actuation. Tailoring of plant stiffness for old and new purposes in agriculture and forestry can be achieved through bioengineering based on the knowledge of the morphological and compositional parameters of plant stiffness in combination with gene identification through the use of genetics. PMID:27457986
Reflectional transformation for structural stiffness
Vashi, K.M.
1990-01-01
This paper presents a structural reflection-related transformation for structural stiffness. The stiffness transformation addresses reflection of a structure about any of the three coordinate planes and renders the desired stiffness matrix using a stiffness matrix for the same structure before reflection. This transformation is elegant and simple, provides an efficient and technically rigorous approach to derive the required stiffness matrix without structural remodeling, and can be readily programmed to quickly perform the required matrix manipulations. 2 figs.
Measuring graphene's bending stiffness
NASA Astrophysics Data System (ADS)
Blees, Melina; Barnard, Arthur; Roberts, Samantha; Kevek, Joshua W.; Ruyack, Alexander; Wardini, Jenna; Ong, Peijie; Zaretski, Aliaksandr; Wang, Siping; McEuen, Paul L.
2013-03-01
Graphene's unusual combination of in-plane strength and out-of-plane flexibility makes it promising for mechanical applications. A key value is the bending stiffness, which microscopic theories and measurements of phonon modes in graphite put at κ0 = 1.2 eV.1 However, theories of the effects of thermal fluctuations in 2D membranes predict that the bending stiffness at longer length scales could be orders of magnitude higher.2,3 This macroscopic value has not been measured. Here we present the first direct measurement of monolayer graphene's bending stiffness, made by mechanically lifting graphene off a surface in a liquid and observing both motion induced by thermal fluctuations and the deflection caused by gravity's effect on added weights. These experiments reveal a value κeff = 12 keV at room temperature -- four orders of magnitude higher than κ0. These results closely match theoretical predictions of the effects of thermally-induced fluctuations which effectively thicken the membrane, dramatically increasing its bending stiffness at macroscopic length scales.
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.
Third Order Elastic Coefficients of Rocks
NASA Astrophysics Data System (ADS)
Bandyopadhyay, K.
2006-12-01
We present a methodology to determine third order elastic (TOE) coefficients of rock from velocity measurements at different hydrostatic stress level. TOE coefficients help us to obtain a quantitative measure of the variation of velocity with stress. It is one of the most general ways to parameterize the stress sensitivity of rocks. We usually determine the isotropic TOE coefficients from measurements of all the independent stiffness elements under non-hydrostatic stress. However, for initially isotropic or weakly anisotropic rocks, most of the laboratory experiments are carried out under hydrostatic stress. In that case, the measurements of P- and S-wave velocities at different hydrostatic pressure alone are not enough to invert for the isotropic TOE parameters. In this underdetermined situation, more information about the rock microstructure causing the non-linearity is required to predict seismic velocities at any arbitrary stress state. Our workflow is based on the model of Mavko et al. (1995) to compute stress-induced anisotropy. This model assumes that the cause of elastic nonlinearity is the presence of compliant crack-like pore. The pressure dependence of generalized compliances is mainly governed by normal tractions resolved across cracks. This assumption allows one to map the pressure dependence from hydrostatic stress to any state of stress. Applying the model of Mavko et al. (1995), we obtain the full stiffness tensor at different non-hydrostatic stress levels from the usual Vp and Vs measurements. Changes in elastic stiffness elements from a reference state of stress are then used to invert for the TOE coefficients, C111, C112 and C123 using the third order stress- strain relations. This method allows us to compute the TOE elements using hydrostatic measurements of an initially isotropic rock. We show an application of the workflow with laboratory measurements of P- and S-wave velocities under varying hydrostatic stress. This enables us to express
Non-axial muscle stress and stiffness.
Zahalak, G I
1996-09-01
A generalization is developed of the classic two-state Huxley cross-bridge model to account for non-axial active stress and stiffness. The main ingredients of the model are: (i) a relation between the general three-dimensional deformation of an element of muscle and the deformations of the cross-bridges, that assumes macroscopic deformation is transmitted to the myofibrils, (ii) radial as well as axial cross-bridge stiffness, and (iii) variations of the attachment and detachment rates with lateral filament spacing. The theory leads to a generalized Huxley rate equation on the bond-distribution function, n(zeta, theta, t), of the form [equation: see text] where the Dij are the components of the relative velocity gradient and rho and ñ are functions of the polar angle, theta, and time that describe, respectively, the deformation of the myofilament lattice and the distribution of accessible actin sites (both of these functions can be calculated from the macroscopic deformation). Explicit expressions, in terms of n, are derived for the nine components of the active stress tensor, and the 21 non-vanishing components of the active stiffness tensor; the active stress tensor is found to be unsymmetric. The theory predicts that in general non-axial deformations will modify active axial stress and stiffness, and also give rise to non-axial (e.g., shearing) components. Under most circumstances the magnitudes of the non-axial stress and stiffness components will be small compared with the axial and, further, the effects of non-axial deformation rates will be small compared with those of the axial rate. Large transverse deformations may, however, greatly reduce the axial force and stiffness. The theory suggests a significant mechanical role for the non-contractile proteins in muscle, namely that of equilibrating the unsymmetric active stresses. Some simple applications of the theory are provided to illustrate its physical content. PMID:8917737
ERIC Educational Resources Information Center
Howell, Ryan T.; Shields, Alan L.
2008-01-01
Meta-analytic reliability generalizations (RGs) are limited by the scarcity of reliability reporting in primary articles, and currently, RG investigators lack a method to quantify the impact of such nonreporting. This article introduces a stepwise procedure to address this challenge. First, the authors introduce a formula that allows researchers…
NASA Astrophysics Data System (ADS)
Zhang, Hai-Qiang; Chen, Jian
2016-04-01
In this paper, we study a higher-order variable coefficient nonlinear Schrödinger (NLS) equation, which plays an important role in the control of the ultrashort optical pulse propagation in nonlinear optical systems. Then, we construct a generalized Darboux transformation (GDT) for the higher-order variable coefficient NLS equation. The Nth order rogue wave solution is obtained by the iterative rule and it can be expressed by the determinant form. As application, we calculate rogue waves (RWs) from first- to fourth-order in accordance with different kinds of parameters. In particular, the dynamical properties and spatial-temporal structures of RWs are discussed and compared with Hirota equation through some figures.
Tectorial Membrane Stiffness Gradients
Richter, Claus-Peter; Emadi, Gulam; Getnick, Geoffrey; Quesnel, Alicia; Dallos, Peter
2007-01-01
The mammalian inner ear processes sound with high sensitivity and fine resolution over a wide frequency range. The underlying mechanism for this remarkable ability is the “cochlear amplifier”, which operates by modifying cochlear micromechanics. However, it is largely unknown how the cochlea implements this modification. Although gradual improvements in experimental techniques have yielded ever-better descriptions of gross basilar membrane vibration, the internal workings of the organ of Corti and of the tectorial membrane have resisted exploration. Although measurements of cochlear function in mice with a gene mutation for α-tectorin indicate the tectorial membrane's key role in the mechanoelectrical transformation by the inner ear, direct experimental data on the tectorial membrane's physical properties are limited, and only a few direct measurements on tectorial micromechanics are available. Using the hemicochlea, we are able to show that a tectorial membrane stiffness gradient exists along the cochlea, similar to that of the basilar membrane. In artificial perilymph (but with low calcium), the transversal and radial driving point stiffnesses change at a rate of –4.0 dB/mm and −4.9 dB/mm, respectively, along the length of the cochlear spiral. In artificial endolymph, the stiffness gradient for the transversal component was –3.4 dB/mm. Combined with the changes in tectorial membrane dimensions from base to apex, the radial stiffness changes would be able to provide a second frequency-place map in the cochlea. Young's modulus, which was obtained from measurements performed in the transversal direction, decreased by −2.6 dB/mm from base to apex. PMID:17496047
Waves in geomaterials exhibiting negative stiffness behaviour
NASA Astrophysics Data System (ADS)
Esin, Maxim; Dyskin, Arcady; Pasternak, Elena
2016-04-01
Negative stiffness denotes the type of material behaviour when the force applied to the body decreases the body's deformation increases. Some geomaterials, for instance, rocks, demonstrate behaviour of this type at certain loads: during the compression tests the loading curves exhibit descending branch (post-peak softening). One of the possible mechanisms of the negative stiffness appearance in geomaterials is rotation of non-spherical grains. It is important to emphasize that in this case the descending branch may be reversible given that the testing machine is stiff enough (in general case it means an importance of boundary conditions). Existence of geomaterials with a negative modulus associated with rotations may have significant importance. In particular, important is understanding of the wave propagation in such materials. We study the stability of geomaterials with negative stiffness inclusions and wave propagation in it using two approaches: Cosserat continuum and discrete mass-spring models. In both cases we consider the rotational degrees of freedom in addition to the conventional translational ones. We show that despite non positiveness of the energy the materials with negative stiffness elements can be stable if certain conditions are met. In the case of Cosserat continuum the Cosserat shear modulus (the modulus relating the non-symmetrical part of shear stress and internal rotations) is allowed to assume negative values as long as its value does not exceed the value of the standard (positive) shear modulus. In the case of discrete mass-spring systems (with translational and rotational springs) the concentration of negative stiffness springs and the absolute values of negative spring stiffness are limited. The critical concentration when the system loses stability and the amplitude of the oscillations tends to infinity is equal to 1/2 and 3/5 for two- and three-dimensional cases respectively.
NASA Astrophysics Data System (ADS)
Basarab-Horwath, P.; Güngör, F.; Özemir, C.
2013-11-01
We consider generalized KP-Burgers equations and attempt to identify subclasses admitting Virasoro or Kac-Moody type algebras as their symmetries. We give reductions to ODEs constructed from invariance requirement under these infinite-dimensional Lie symmetry algebras and integrate them in cases where it is possible. We also look at the conditions under which the equation passes the Painlevé test and construct some exact solutions by truncation.
Orbai, Ana-Maria; Smith, Katherine C.; Bartlett, Susan J.; De Leon, Elaine; Bingham, Clifton O.
2014-01-01
Objective Stiffness is a well-recognized symptom of Rheumatoid Arthritis (RA). It is frequently queried during clinic visits as an indicator of disease activity, and was included in the 1961 and 1987 RA classification criteria. Little is known about how people with RA experience stiffness and its impact on their lives. Methods We conducted 4 focus groups with 20 people with RA (4-6 participants per group), from one academic clinical practice and one private practice, to generate accounts of stiffness experiences. Qualitative inductive thematic data analysis was conducted. Results Five overarching themes were identified: 1. Relationship of stiffness with other symptoms; 2. Exacerbating or alleviating factors and self-management; 3. Stiffness timing and location; 4. Individual meanings of stiffness experiences; 5. Impact of stiffness on daily life. Conclusion Focus group discussions revealed individual stiffness experiences as diverse and complex. Several stiffness features were endorsed by a majority of participants, but few, if any, were universally experienced, thus the significance of stiffness as an expression of the disease varied widely. Discussions yielded descriptions of how individual limits imposed by RA in general and stiffness in particular, may change over time and were intertwined with adaptations to preserve participation in valued life activities. These results concerning the diversity of the stiffness experience, consequential adaptations, and its impact suggest a more individualized approach to stiffness measurement may be needed in order to improve stiffness assessments. PMID:24891304
Horváth, Tamás; Osztovits, János; Pintér, Alexandra; Littvay, Levente; Cseh, Domonkos; Tárnoki, Adám D; Tárnoki, Dávid L; Jermendy, Adám L; Steinbach, Rita; Métneki, Júlia; Schillaci, Giuseppe; Kollai, Márk; Jermendy, György
2014-01-01
Arterial stiffness is an independent predictor of cardiovascular, cerebrovascular and all-cause mortality. Quantifying the genetic influence on the stiff arterial phenotype allows us to better predict the development of arterial stiffness. In this study, we aimed to determine the heritability of carotid artery stiffness in healthy twins. We studied 98 twin pairs of both sexes. We determined carotid artery stiffness locally using echo tracking and applanation tonometry. We estimated the heritability of stiffness parameters using structural equation modeling. The carotid distensibility coefficient showed the highest heritability (64%, 95% confidence interval 45-77%). The incremental elastic modulus, compliance and stiffness index β also showed substantial heritability (62%, 61% and 58%, respectively). The remaining 36-42% phenotypic variance was attributed to unshared environmental effects. Genetic influence appears to dominate over environmental factors in the development of carotid artery stiffness. Environmental factors may have an important role in favorably influencing the genetic predisposition for accelerated arterial stiffening. PMID:24089266
NASA 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.
NASA Astrophysics Data System (ADS)
Zayed, Elsayed M. E.; Abdelaziz, Mahmoud A. M.
2010-12-01
In this article, a generalized (Ǵ/G)-expansion method is used to find exact travelling wave solutions of the Burgers equation and the Korteweg-de Vries (KdV) equation with variable coefficients. As a result, hyperbolic, trigonometric, and rational function solutions with parameters are obtained. When these parameters are taking special values, the solitary wave solutions are derived from the hyperbolic function solution. It is shown that the proposed method is direct, effective, and can be applied to many other nonlinear evolution equations in mathematical physics.
Rea, A.H.; Tortorelli, R.L.
1997-01-01
This digital report contains two digital-map grids of data that were used to develop peak-flow regression equations in Tortorelli, 1997, 'Techniques for estimating peak-streamflow frequency for unregulated streams and streams regulated by small floodwater retarding structures in Oklahoma,' U.S. Geological Survey Water-Resources Investigations Report 97-4202. One data set is a grid of mean annual precipitation, in inches, based on the period 1961-90, for Oklahoma. The data set was derived from the PRISM (Parameter-elevation Regressions on Independent Slopes Model) mean annual precipitation grid for the United States, developed by Daly, Neilson, and Phillips (1994, 'A statistical-topographic model for mapping climatological precipitation over mountainous terrain:' Journal of Applied Meteorology, v. 33, no. 2, p. 140-158). The second data set is a grid of generalized skew coefficients of logarithms of annual maximum streamflow for Oklahoma streams less than or equal to 2,510 square miles in drainage area. This grid of skew coefficients is taken from figure 11 of Tortorelli and Bergman, 1985, 'Techniques for estimating flood peak discharges for unregulated streams and streams regulated by small floodwater retarding structures in Oklahoma,' U.S. Geological Survey Water-Resources Investigations Report 84-4358. To save disk space, the skew coefficient values have been multiplied by 100 and rounded to integers with two significant digits. The data sets are provided in an ASCII grid format.
NASA Astrophysics Data System (ADS)
Xie, Xi-Yang; Tian, Bo; Sun, Wen-Rong; Sun, Ya; Liu, De-Yin
2015-10-01
In this paper, we construct soliton solutions for a generalized variable-coefficient coupled Hirota-Maxwell-Bloch system, which can describe the ultrashort optical pulse propagation in a nonlinear, dispersive fiber doped with two-level resonant atoms. Under certain transformations and constraints, one- and two-soliton solutions are obtained via the Hirota method and symbolic computation, and soliton collisions are graphically presented and analyzed. One soliton is shown to maintain its amplitude and shape during the propagation. Soliton collision is elastic, while bright two-peak solitons and dark two-peak solitons are also observed. We discuss the influence of the coefficients for the group velocity, group-velocity dispersion (GVD), self-phase modulation, distribution of the dopant, and Stark shift on the soliton propagation and collision features, with those coefficients are set as some constants and functions, respectively. We find the group velocity and self-phase modulation can change the solitons' amplitudes and widths, and the solitons become curved when the GVD and distribution of the dopant are chosen as some functions. When the Stark shift is chosen as a certain constant, the two peaks of bright two-peak solitons and dark two-peak solitons are not parallel. In addition, we observe the periodic collision of the two solitons.
Properties of the grasp stiffness matrix and conservative control strategies
Kao, I.; Ngo, C.
1999-02-01
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: constant and configuration-dependent matrices. The symmetric part of a constant-stiffness matrix can be derived from a conservative quadratic potential function in the Hermitian form; while the skew-symmetric part is a function of the nonconservative curl vector field of the grasp. A configuration-dependent stiffness matrix needs to be symmetric and must simultaneously satisfy the exact differential condition to be conservative. The theory is most relevant to the Cartesian stiffness control, where the stiffness of the end effector is usually constant, such as that in RCC wrists. Conservative control strategies are proposed for a configuration-dependent stiffness matrix. One of the most important results of this paper is the nonconservative congruence mapping of stiffness between the joint and Cartesian spaces. In general, the congruence transformation (or its inverse transformation), K{sub {theta}} = J{sub {theta}}{sup T}K{sub p}J{sub {theta}}, is a nonconservative mapping over finite paths for a configuration-dependent Jacobian. Thus, to obtain a conservative system with respect to the Cartesian space, one has to either find the corresponding K{sub {theta}} at every configuration due to the constant and symmetric Cartesian stiffness matrix, or determine symmetric yet configuration-varying K{sub {theta}} at every configuration due to the constant and symmetric Cartesian stiffness matrix, or determine the symmetric yet configuration-varying K{sub {theta}} which makes the resulting configuration-dependent K{sub p
Dynamically variable negative stiffness structures.
Churchill, Christopher B; Shahan, David W; Smith, Sloan P; Keefe, Andrew C; McKnight, Geoffrey P
2016-02-01
Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness-based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators. PMID:26989771
Molecular Stiffness of Selectins*
Sarangapani, Krishna K.; Marshall, Bryan T.; McEver, Rodger P.; Zhu, Cheng
2011-01-01
During inflammation, selectin-ligand interactions provide forces for circulating leukocytes to adhere to vascular surfaces, which stretch the interacting molecules, suggesting that mechanical properties may be pertinent to their biological function. From mechanical measurements with atomic force microscopy, we analyzed the molecular characteristics of selectins complexed with ligands and antibodies. Respective stiffness of L-, E-, and P-selectins (4.2, 1.4, and 0.85 piconewton/nm) correlated inversely with the number (2, 6, and 9) of consensus repeats in the selectin structures that acted as springs in series to dominate their compliance. After reconstitution into a lipid bilayer, purified membrane P-selectin remained a dimer, capable of forming dimeric bonds with P-selectin glycoprotein ligand (PSGL)-1, endoglycan-Ig, and a dimeric form of a glycosulfopeptide modeled after the N terminus of PSGL-1. By comparison, purified membrane L- and E-selectin formed only monomeric bonds under identical conditions. Ligands and antibodies were much less stretchable than selectins. The length of endoglycan-Ig was found to be 51 ± 12 nm. These results provide a comprehensive characterization of the molecular stiffness of selectins and illustrate how mechanical measurements can be utilized for molecular analysis, e.g. evaluating the multimericity of selectins and determining the molecular length of endoglycan. PMID:21216951
Dynamically variable negative stiffness structures
Churchill, Christopher B.; Shahan, David W.; Smith, Sloan P.; Keefe, Andrew C.; McKnight, Geoffrey P.
2016-01-01
Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness–based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators. PMID:26989771
Arterial Stiffness and Chronic Kidney Disease
Garnier, Anne-Sophie; Briet, Marie
2016-01-01
Chronic kidney disease (CKD) is a major public health concern due to the high prevalence of associated cardiovascular (CV) disease. CV mortality is 10-30 times higher in end-stage renal disease patients than in the age-adjusted general population. The last 20 years have been marked by a huge effort in the characterization of the vascular remodeling process associated with CKD and its consequences on the renal, CV and general prognosis. By comparison with patients with normal renal function, with or without hypertension, an increase in large artery stiffness has been described in end-stage renal disease as well as in CKD stages 2-5. Most clinical studies are consistent with the observation that damage to large arteries may contribute to the high incidence of CV disease. By contrast, the impact of large artery stiffening and remodeling on CKD progression is still a matter of debate. Concomitant exposure to other CV risk factors, including diabetes, seems to play a major role in the association between aortic stiffness and estimated GFR. The conflicting results obtained from longitudinal studies designed to evaluate the impact of baseline aortic stiffness on GFR progression are detailed in the present review. Only pulse pressure, central and peripheral, is almost constantly associated with incident CKD and GFR decline. Kidney transplantation improves patients’ CV prognosis, but its impact on arterial stiffness is still controversial. Donor age, living kidney donation and mean blood pressure appear to be the main determinants of improvement in aortic stiffness after kidney transplantation. PMID:27195244
Implicit Extrapolation Methods for Variable Coefficient Problems
NASA Technical Reports Server (NTRS)
Jung, M.; Ruede, U.
1996-01-01
Implicit extrapolation methods for the solution of partial differential equations are based on applying the extrapolation principle indirectly. Multigrid tau-extrapolation is a special case of this idea. In the context of multilevel finite element methods, an algorithm of this type can be used to raise the approximation order, even when the meshes are nonuniform or locally refined. Here previous results are generalized to the variable coefficient case and thus become applicable for nonlinear problems. The implicit extrapolation multigrid algorithm converges to the solution of a higher order finite element system. This is obtained without explicitly constructing higher order stiffness matrices but by applying extrapolation in a natural form within the algorithm. The algorithm requires only a small change of a basic low order multigrid method.
NASA Astrophysics Data System (ADS)
Tu, Jian-Min; Tian, Shou-Fu; Xu, Mei-Juan; Ma, Pan-Li
2015-07-01
In this paper, a (2 + 1)-dimensional generalized variable-coefficient Sawada-Kotera (gvcSK) equation is investigated, which describes many nonlinear phenomena in fluid dynamics and plasma physics. Based on the properties of binary Bell polynomials, we present a Hirota’s bilinear equation to the gvcSK equation. By virtue of the Hirota’s bilinear equation, we obtain the N-soliton solutions and the quasi-periodic wave solutions of the gvcSK equation, which can be reduced to the ones of several integrable equations such as Sawada-Kotera, modified Caudrey-Dodd-Gibbon-Sawada-Kotera, isospectral BKP equations and etc. Furthermore, we obtain the relationship between the soliton solutions and periodic solutions by considering the asymptotic properties of the periodic solutions.
Dynamic stiffness removal for direct numerical simulations
Lu, Tianfeng; Law, Chung K.; Yoo, Chun Sang; Chen, Jacqueline H.
2009-08-15
A systematic approach was developed to derive non-stiff reduced mechanisms for direct numerical simulations (DNS) with explicit integration solvers. The stiffness reduction was achieved through on-the-fly elimination of short time-scales induced by two features of fast chemical reactivity, namely quasi-steady-state (QSS) species and partial-equilibrium (PE) reactions. The sparse algebraic equations resulting from QSS and PE approximations were utilized such that the efficiency of the dynamic stiffness reduction is high compared with general methods of time-scale reduction based on Jacobian decomposition. Using the dimension reduction strategies developed in our previous work, a reduced mechanism with 52 species was first derived from a detailed mechanism with 561 species. The reduced mechanism was validated for ignition and extinction applications over the parameter range of equivalence ratio between 0.5 and 1.5, pressure between 10 and 50 atm, and initial temperature between 700 and 1600 K for ignition, and worst-case errors of approximately 30% were observed. The reduced mechanism with dynamic stiffness removal was then applied in homogeneous and 1-D ignition applications, as well as a 2-D direct numerical simulation of ignition with temperature inhomogeneities at constant volume with integration time-steps of 5-10 ns. The integration was numerically stable and good accuracy was achieved. (author)
NASA Astrophysics Data System (ADS)
Collier, Craig S.
1993-04-01
A method is presented for formulating stiffness terms and thermal coefficients of stiffened, fiber-reinforced composite panels. The method is robust enough to handle panels with general cross sectional shapes, including those which are unsymmetric and/or unbalanced. Nonlinear, temperature and load dependent constitutive material data of each laminate are used to 'build-up' the stiffened panel membrane, bending, and membrane-bending coupling stiffness terms and thermal coefficients. New thermal coefficients are introduced to quantify panel response from through-the-thickness temperature gradients. A technique of implementing this capability with a single plane of shell finite elements using the MSC/NASTRAN analysis program (FEA) is revealed that provides accurate solutions of entire airframes or engines with coarsely meshed models. An example of a composite, hat-stiffened panel is included to demonstrate errors that occur when an unsymmetric panel is symmetrically formulated as traditionally done. The erroneous results and the correct ones produced from this method are compared to analysis from discretely meshed three-dimensional FEA.
NASA Technical Reports Server (NTRS)
Collier, Craig S.
1993-01-01
A method is presented for formulating stiffness terms and thermal coefficients of stiffened, fiber-reinforced composite panels. The method is robust enough to handle panels with general cross sectional shapes, including those which are unsymmetric and/or unbalanced. Nonlinear, temperature and load dependent constitutive material data of each laminate are used to 'build-up' the stiffened panel membrane, bending, and membrane-bending coupling stiffness terms and thermal coefficients. New thermal coefficients are introduced to quantify panel response from through-the-thickness temperature gradients. A technique of implementing this capability with a single plane of shell finite elements using the MSC/NASTRAN analysis program (FEA) is revealed that provides accurate solutions of entire airframes or engines with coarsely meshed models. An example of a composite, hat-stiffened panel is included to demonstrate errors that occur when an unsymmetric panel is symmetrically formulated as traditionally done. The erroneous results and the correct ones produced from this method are compared to analysis from discretely meshed three-dimensional FEA.
NASA Astrophysics Data System (ADS)
Suk, Heejun
2016-08-01
This paper presents a semi-analytical procedure for solving coupled the multispecies reactive solute transport equations, with a sequential first-order reaction network on spatially or temporally varying flow velocities and dispersion coefficients involving distinct retardation factors. This proposed approach was developed to overcome the limitation reported by Suk (2013) regarding the identical retardation values for all reactive species, while maintaining the extensive capability of the previous Suk method involving spatially variable or temporally variable coefficients of transport, general initial conditions, and arbitrary temporal variable inlet concentration. The proposed approach sequentially calculates the concentration distributions of each species by employing only the generalized integral transform technique (GITT). Because the proposed solutions for each species' concentration distributions have separable forms in space and time, the solution for subsequent species (daughter species) can be obtained using only the GITT without the decomposition by change-of-variables method imposing the limitation of identical retardation values for all the reactive species by directly substituting solutions for the preceding species (parent species) into the transport equation of subsequent species (daughter species). The proposed solutions were compared with previously published analytical solutions or numerical solutions of the numerical code of the Two-Dimensional Subsurface Flow, Fate and Transport of Microbes and Chemicals (2DFATMIC) in three verification examples. In these examples, the proposed solutions were well matched with previous analytical solutions and the numerical solutions obtained by 2DFATMIC model. A hypothetical single-well push-pull test example and a scale-dependent dispersion example were designed to demonstrate the practical application of the proposed solution to a real field problem.
Kengne, E.; Lakhssassi, A.; Vaillancourt, R.; Liu, Wu-Ming
2012-12-15
We present a double-mapping method (D-MM), a natural combination of a similarity with F-expansion methods, for obtaining general solvable nonlinear evolution equations. We focus on variable-coefficients complex Ginzburg-Landau equations (VCCGLE) with multi-body interactions. We show that it is easy by this method to find a large class of exact solutions of Gross-Pitaevskii and Gross-Pitaevskii-Ginzburg equations. We apply the D-MM to investigate the dynamics of Bose-Einstein condensation with two- and three-body interactions. As a surprising result, we obtained that it is very easy to use the built D-MM to obtain a large class of exact solutions of VCCGLE with two-body interactions via a generalized VCCGLE with two- and three-body interactions containing cubic-derivative terms. The results show that the proposed method is direct, concise, elementary, and effective, and can be a very effective and powerful mathematical tool for solving many other nonlinear evolution equations in physics.
An Imageless Ultrasound Device to Measure Local and Regional Arterial Stiffness.
Sahani, Ashish Kumar; Shah, Malay Ilesh; Radhakrishnan, Ravikumar; Joseph, Jayaraj; Sivaprakasam, Mohanasankar
2016-02-01
Arterial stiffness (AS) has been shown to be an important marker for risk assessment of cardiovascular events. Local arterial stiffness (LAS) is conventionally measured by evaluating arterial distensibility at particular arterial sites through ultrasound imaging systems. Regional arterial stiffness (RAS) is generally obtained by evaluating carotid to femoral pulse wave velocity (cfPWV) through tonometric devices. RAS has a better prognostic value than LAS and cfPWV is considered as the gold standard of AS. Over the past few years our group has been developing ARTerial Stiffness Evaluation for Non-Invasive Screening (ARTSENS), an inexpensive and portable device to measure the LAS. It uses a single element ultrasound transducer to obtain A-Mode frames from the desired artery and is fully automated to enable a non-expert to perform measurements. In this work, we report an extension of ARTSENS to enable measurement of cfPWV that now makes it the only fully automatic device that can measure both LAS and RAS. In this paper, we provide a general review of the ARTSENS and compare it with other state-of-the-art AS measurement systems. cfPWV measurement using ARTSENS was cross-validated against SphygmoCor by successive measurements with both devices on 41 human subjects and excellent agreement between both devices was demonstrated (Coefficient of determination and, limits of agreement m/s). The inter-device correlation between ARTSENS and SphygmoCor was found to be better than other similar studies reported in the literature. PMID:25775498
Stiffness adaptations in shod running.
Divert, Carolyn; Baur, Heiner; Mornieux, Guillaume; Mayer, Frank; Belli, Alain
2005-11-01
When mechanical parameters of running are measured, runners have to be accustomed to testing conditions. Nevertheless, habituated runners could still show slight evolutions of their patterns at the beginning of each new running bout. This study investigated runners' stiffness adjustments during shoe and barefoot running and stiffness evolutions of shoes. Twenty-two runners performed two 4-minute bouts at 3.61 m.s-1 shod and barefoot after a 4-min warm-up period. Vertical and leg stiffness decreased during the shoe condition but remained stable in the barefoot condition, p < 0.001. Moreover, an impactor test showed that shoe stiffness increased significantly during the first 4 minutes, p < 0.001. Beyond the 4th minute, shoe properties remained stable. Even if runners were accustomed to the testing condition, as running pattern remained stable during barefoot running, they adjusted their leg and vertical stiffness during shoe running. Moreover, as measurements were taken after a 4-min warm-up period, it could be assumed that shoe properties were stable. Then the stiffness adjustment observed during shoe running might be due to further habituations of the runners to the shod condition. To conclude, it makes sense to run at least 4 minutes before taking measurements in order to avoid runners' stiffness alteration due to shoe property modifications. However, runners could still adapt to the shoe. PMID:16498177
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
Fluid damping and fluid stiffness of tube arrays in crossflow
Chen, S.S.; Zhu, S.; Jendrzejczyk, J.A.
1994-06-01
Motion-dependent fluid forces acting on a tube array were measured as a function of excitation frequency, excitation amplitude, and flow velocity. Fluid-damping and fluid-stiffness coefficients were obtained from measured motion-dependent fluid forces as a function of reduced flow velocity and excitation amplitude. The water channel and test setup provide a sound facility for obtaining key coefficients for fluidelastic instability of tube arrays in crossflow. Once the motion-dependent fluid-force coefficients have been measured, a reliable design guideline, based on the unsteady flow theory, can be developed for fluidelastic instability of tube arrays in crossflow.
Time simulation of flutter with large stiffness changes
NASA Technical Reports Server (NTRS)
Karpel, Mordechay; Wieseman, Carol D.
1992-01-01
Time simulation of flutter, involving large local structural changes, is formulated with a state-space model that is based on a relatively small number of generalized coordinates. Free-free vibration modes are first calculated for a nominal finite-element model with relatively large fictitious masses located at the area of structural changes. A low-frequency subset of these modes is then transformed into a set of structural modal coordinates with which the entire simulation is performed. These generalized coordinates and the associated oscillatory aerodynamic force coefficient matrices are used to construct an efficient time-domain, state-space model for a basic aeroelastic case. The time simulation can then be performed by simply changing the mass, stiffness, and damping coupling terms when structural changes occur. It is shown that the size of the aeroelastic model required for time simulation with large structural changes at a few apriori known locations is similar to that required for direct analysis of a single structural case. The method is applied to the simulation of an aeroelastic wind-tunnel model. The diverging oscillations are followed by the activation of a tip-ballast decoupling mechanism that stabilizes the system but may cause significant transient overshoots.
Time simulation of flutter with large stiffness changes
NASA Technical Reports Server (NTRS)
Karpel, M.; Wieseman, C. D.
1992-01-01
Time simulation of flutter, involving large local structural changes, is formulated with a state-space model that is based on a relatively small number of generalized coordinates. Free-free vibration modes are first calculated for a nominal finite-element model with relatively large fictitious masses located at the area of structural changes. A low-frequency subset of these modes is then transformed into a set of structural modal coordinates with which the entire simulation is performed. These generalized coordinates and the associated oscillatory aerodynamic force coefficient matrices are used to construct an efficient time-domain, state-space model for basic aeroelastic case. The time simulation can then be performed by simply changing the mass, stiffness and damping coupling terms when structural changes occur. It is shown that the size of the aeroelastic model required for time simulation with large structural changes at a few a priori known locations is similar to that required for direct analysis of a single structural case. The method is applied to the simulation of an aeroelastic wind-tunnel model. The diverging oscillations are followed by the activation of a tip-ballast decoupling mechanism that stabilizes the system but may cause significant transient overshoots.
NASA Technical Reports Server (NTRS)
Nelson, C. C.; Childs, D. W.; Nicks, C.; Elrod, D.
1985-01-01
The leakage and rotordynamic coefficients of constant-clearance and convergent-tapered annular gas seals were measured in an experimental test facility. The results are presented along with the theoretically predicted values. Of particular interest is the prediction that optimally tapered seals have significantly larger direct siffness than straight seals. The experimental results verify this prediction. Generally the theory does quite well, but fails to predict the large increase in direct stiffness when the fluid is pre-rotated.
Wassenaar, Peter A; Eleswarpu, Chethanya N; Schroeder, Samuel A; Mo, Xiaokui; Raterman, Brian D; White, Richard D; Kolipaka, Arunark
2015-01-01
Purpose To assess reproducibility in measuring left ventricular (LV) myocardial stiffness in volunteers throughout the cardiac cycle using magnetic resonance elastography (MRE) and to determine its correlation with age. Methods Cardiac MRE (CMRE) was performed on 29 normal volunteers, with ages ranging from 21 to 73 years. For assessing reproducibility of CMRE-derived stiffness measurements, scans were repeated per volunteer. Wave images were acquired throughout the LV myocardium, and were analyzed to obtain mean stiffness during the cardiac cycle. CMRE-derived stiffness values were correlated to age. Results Concordance correlation coefficient revealed good inter-scan agreement with rc of 0.77, with p-value<0.0001. Significantly higher myocardial stiffness was observed during end-systole (ES) compared to end-diastole (ED) across all subjects. Additionally, increased deviation between ES and ED stiffness was observed with increased age. Conclusion CMRE-derived stiffness is reproducible, with myocardial stiffness changing cyclically across the cardiac cycle. Stiffness is significantly higher during ES compared to ED. With age, ES myocardial stiffness increases more than ED, giving rise to an increased deviation between the two. PMID:26010456
Evaluation of Arterial Stiffness by Echocardiography: Methodological Aspects
Cho, Jae Yeong
2016-01-01
As humans age, degenerative changes in the arterial structure gradually progress and result in the stiffening of the arteries, which is called arteriosclerosis. Arterial stiffness is now an established risk factor of cardiovascular disease (CVD). This stiffening has adverse effects for both the general population as well as for patients with CVD. Measurements of pulse wave velocity and pulse wave analysis are the two most commonly used methods in the evaluation of arterial stiffness, but these methods just allow indirect measures of arterial stiffness. Echocardiography is the most widely used imaging modality in the evaluation of cardiac structure and function and with recent technical advances, it has become possible to evaluate the structure, function and blood flow hemodynamics of the arteries using echocardiography. In the present review, we will discuss the current status of echocardiography in the evaluation of arterial stiffness, especially focusing on the methodological aspects. PMID:27231673
ARTHROSCOPIC TREATMENT OF ELBOW STIFFNESS
Vieira, Luis Alfredo Gómez; Dal Molin, Fabio Farina; Visco, Adalberto; Fernandes, Luis Filipe Daneu; dos Santos, Murilo Cunha Rafael; Cardozo Filho, Nivaldo Souza; Gómez Cordero, Nicolas Gerardo
2015-01-01
To present the arthroscopic surgical technique and the evaluation of the results from this technique for treating elbow stiffness. Methods: Between April 2007 and January 2010, ten elbows of ten patients with elbow stiffness underwent arthroscopic treatment to release the range of motion. The minimum follow-up was 11 months, with an average of 27 months. All the patients were male and their average age was 32.8 years (ranging from 22 to 48 years). After the arthroscopic treatment, they were followed up weekly in the first month and every three months thereafter. The clinical evaluation was made using the criteria of the University of California at Los Angeles (UCLA). Results: All the patients were satisfied with the results from the arthroscopic treatment. The average UCLA score was 33.8 points. Conclusion: Arthroscopic treatment for elbow stiffness is a minimally invasive surgical technique that was shown to be efficient for treating this complication. PMID:27027027
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.
Cosmology with a stiff matter era
NASA Astrophysics Data System (ADS)
Chavanis, Pierre-Henri
2015-11-01
We consider the possibility that the Universe is made of a dark fluid described by a quadratic equation of state P =K ρ2 , where ρ is the rest-mass density and K is a constant. The energy density ɛ =ρ c2+K ρ2 is the sum of two terms: a rest-mass term ρ c2 that mimics "dark matter" (P =0 ) and an internal energy term u =K ρ2=P that mimics a "stiff fluid" (P =ɛ ) in which the speed of sound is equal to the speed of light. In the early universe, the internal energy dominates and the dark fluid behaves as a stiff fluid (P ˜ɛ , ɛ ∝a-6). In the late universe, the rest-mass energy dominates and the dark fluid behaves as pressureless dark matter (P ≃0 , ɛ ∝a-3). We provide a simple analytical solution of the Friedmann equations for a universe undergoing a stiff matter era, a dark matter era, and a dark energy era due to the cosmological constant. This analytical solution generalizes the Einstein-de Sitter solution describing the dark matter era, and the Λ CDM model describing the dark matter era and the dark energy era. Historically, the possibility of a primordial stiff matter era first appeared in the cosmological model of Zel'dovich where the primordial universe is assumed to be made of a cold gas of baryons. A primordial stiff matter era also occurs in recent cosmological models where dark matter is made of relativistic self-gravitating Bose-Einstein condensates (BECs). When the internal energy of the dark fluid mimicking stiff matter is positive, the primordial universe is singular like in the standard big bang theory. It expands from an initial state with a vanishing scale factor and an infinite density. We consider the possibility that the internal energy of the dark fluid is negative (while, of course, its total energy density is positive), so that it mimics anti-stiff matter. This happens, for example, when the BECs have an attractive self-interaction with a negative scattering length. In that case, the primordial universe is nonsingular and
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
Criterion validity of manual assessment of spinal stiffness.
Koppenhaver, Shane L; Hebert, Jeffrey J; Kawchuk, Greg N; Childs, John D; Teyhen, Deydre S; Croy, Theodore; Fritz, Julie M
2014-12-01
Assessment of spinal stiffness is widely used by manual therapy practitioners as a part of clinical diagnosis and treatment selection. Although studies have commonly found poor reliability of such procedures, conflicting evidence suggests that assessment of spinal stiffness may help predict response to specific treatments. The current study evaluated the criterion validity of manual assessments of spinal stiffness by comparing them to indentation measurements in patients with low back pain (LBP). As part of a standard examination, an experienced clinician assessed passive accessory spinal stiffness of the L3 vertebrae using posterior to anterior (PA) force on the spinous process of L3 in 50 subjects (54% female, mean (SD) age = 33.0 (12.8) years, BMI = 27.0 (6.0) kg/m(2)) with LBP. A criterion measure of spinal stiffness was performed using mechanized indentation by a blinded second examiner. Results indicated that manual assessments were uncorrelated to criterion measures of stiffness (spearman rho = 0.06, p = 0.67). Similarly, sensitivity and specificity estimates of judgments of hypomobility were low (0.20-0.45) and likelihood ratios were generally not statistically significant. Sensitivity and specificity of judgments of hypermobility were not calculated due to limited prevalence. Additional analysis found that BMI explained 32% of the variance in the criterion measure of stiffness, yet failed to improve the relationship between assessments. Additional studies should investigate whether manual assessment of stiffness relates to other clinical and biomechanical constructs, such as symptom reproduction, angular rotation, quality of motion, or end feel. PMID:24965495
Modulation of ankle stiffness during postural sway.
Lang, Christopher B; Kearney, Robert E
2014-01-01
Ankle stiffness is a nonlinear, time-varying system which contributes to the control of human upright stance. This study sought to examine the nature of the contribution of stiffness to postural control by determining how intrinsic and reflex stiffnesses varied with sway. Subjects were instructed to stand quietly on a bilateral electro-hydraulic actuator while perturbations were applied about the ankle. Subjects performed three types of trials: normal stance, forward lean, and backward lean. Position, torque, and EMGs from the tibialis anterior and triceps surae were recorded. Background torque, intrinsic stiffness and reflex stiffness were calculated for each perturbation. Intrinsic and reflex stiffnesses were heavily modulated by postural sway. Moreover, they were modulated in a complimentary manner; intrinsic stiffness was lowest when reflex gain was highest, and vice versa. These findings suggest that intrinsic stiffness is modulated simultaneously with reflex stiffness to optimize the control of balance. PMID:25570884
Bending Stiffness of Multiwall Sandwich
NASA Technical Reports Server (NTRS)
Blosser, M. L.
1983-01-01
An analytical and experimental study was carried out to understand the extensional and flexural behavior of multiwall sandwich, a metallic insulation composed of alternate layers of flat and dimpled foil. The multiwall sandwich was structurally analyzed by using several simplifying assumptions combined with a finite element analysis. The simplifying assumptions made in this analysis were evaluated by bending and tensile tests. Test results validate the assumption that flat sheets in compression do not significantly contribute to the flexural stiffness of multiwall sandwich for the multiwall geometry tested. However, calculations show that thicker flat sheets may contribute significantly to bending stiffness and cannot be ignored. Results of this analytical approach compare well with test data; both show that the extensional stiffness of the dimpled sheet in he 0 deg direction is about 30 percent of that for a flat sheet, and that in the 45 deg direction, it is about 10 percent. The analytical and experimental multiwall bending stiffness showed good agreement for the particular geometry tested.
Stiffness of Diphenylalanine-Based Molecular Solids from First Principles Calculations
NASA Astrophysics Data System (ADS)
Azuri, Ido; Hod, Oded; Gazit, Ehud; Kronik, Leeor
2013-03-01
Diphenylalanine-based peptide nanotubes were found to be unexpectedly stiff, with a Young modulus of 19 GPa. Here, we calculate the Young modulus from first principles, using density functional theory with dispersive corrections. This allows us to show that at least half of the stiffness of the material comes from dispersive interactions and to identify the nature of the interactions that contribute most to the stiffness. This presents a general strategy for the analysis of bioinspired functional materials.
NASA Astrophysics Data System (ADS)
Zhang, Yi; Xu, Yue; Ma, Kun
2016-08-01
In this paper, the variable-coefficient Kadomtsev-Petviashvili (vcKP) equation with self-consistent sources is presented by two different methods, one is the source generation procedure, the other is the Pfaffianization procedure, and the solutions for the two new coupled systems are given through Grammian-type Pfaffian determinants.
“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
A NASTRAN DMAP alter for determining a local stiffness modification to obtain a specified eigenvalue
NASA Technical Reports Server (NTRS)
Case, W. R., Jr.
1973-01-01
A technique is described which has been programmed as a DMAP Alter to Rigid Format 3, for determining a stiffness matrix modification to obtain a specified eigenvalue for a structure. The stiffness matrix modifications allowable are those that can be described as the product of a single scalar variable and a matrix of constant coefficients input by the user. The program solves for the scalar variable multiplier which will yield a specified eigenvalue for the complete structure (provided it exists), makes the modification to the stiffness matrix, and proceeds in Rigid Format 3 to obtain the eigenvalues and eigenvectors of the modified structure.
Experimental 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 to 30,000 rpm and gas supply pressure ratios to 4.8. From measured amplitude and phase angle data, dynamic stiffness and damping coefficients of the bearings were determined. The measured stiffness was proportional to the supply pressure, while damping was little affected by supply pressure. Damping dropped rapidly as the fractional frequency whirl threshold was approached. A small-eccentricity analysis overpredicted the stiffness by 20 to 70 percent. Predicted damping was lower than measured at low speeds but higher at high speeds.
Calculation of exact vibration modes for plane grillages by the dynamic stiffness method
NASA Technical Reports Server (NTRS)
Hallauer, W. L., Jr.; Liu, R. Y. L.
1982-01-01
A dynamic stiffness method is developed for the calculation of the exact modal parameters for plane grillages which consist of straight and uniform beams with coincident elastic and inertial axes. Elementary bending-torsion beam theory is utilized, and bending translation is restricted to one direction. The exact bending-torsion dynamic stiffness matrix is obtained for a straight and uniform beam element with coincident elastic and inertial axes. The element stiffness matrices are assembled using the standard procedure of the static stiffness method to form the dynamic stiffness matrix of the complete grillage. The exact natural frequencies, mode shapes, and generalized masses of the grillage are then calculated by solving a nonlinear eigenvalue problem based on the dynamic stiffness matrix. The exact modal solutions for an example grillage are calculated and compared with the approximate solutions obtained by using the finite element method.
Order stars and stiff integrators
NASA Astrophysics Data System (ADS)
Hairer, Ernst; Wanner, Gerhard
2000-12-01
Order stars, introduced in G. Wanner, E. Hairer, S.P. Nørsett (Order stars and stability theorems, BIT 18 (1978) 475-489), have become a fundamental tool for the understanding of order and stability properties of numerical methods for stiff differential equations. This survey retraces their discovery and their principal achievements. We also sketch some later extensions and describe some recent developments.
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.; Mikulas, Martin M., Jr.
2009-01-01
Simple formulas for the buckling stress of homogeneous, specially orthotropic, laminated-composite cylinders are presented. The formulas are obtained by using nondimensional parameters and equations that facilitate general validation, and are validated against the exact solution for a wide range of cylinder geometries and laminate constructions. Results are presented that establish the ranges of the nondimensional parameters and coefficients used. General results, given in terms of the nondimensional parameters, are presented that encompass a wide range of geometries and laminate constructions. These general results also illustrate a wide spectrum of behavioral trends. Design-oriented results are also presented that provide a simple, clear indication of laminate composition on critical stress, critical strain, and axial stiffness. An example is provided to demonstrate the application of these results to thin-walled column designs.
Elastic metamaterial beam with remotely tunable stiffness
NASA Astrophysics Data System (ADS)
Qian, Wei; Yu, Zhengyue; Wang, Xiaole; Lai, Yun; Yellen, Benjamin B.
2016-02-01
We demonstrate a dynamically tunable elastic metamaterial, which employs remote magnetic force to adjust its vibration absorption properties. The 1D metamaterial is constructed from a flat aluminum beam milled with a linear array of cylindrical holes. The beam is backed by a thin elastic membrane, on which thin disk-shaped permanent magnets are mounted. When excited by a shaker, the beam motion is tracked by a Laser Doppler Vibrometer, which conducts point by point scanning of the vibrating element. Elastic waves are unable to propagate through the beam when the driving frequency excites the first elastic bending mode in the unit cell. At these frequencies, the effective mass density of the unit cell becomes negative, which induces an exponentially decaying evanescent wave. Due to the non-linear elastic properties of the membrane, the effective stiffness of the unit cell can be tuned with an external magnetic force from nearby solenoids. Measurements of the linear and cubic static stiffness terms of the membrane are in excellent agreement with experimental measurements of the bandgap shift as a function of the applied force. In this implementation, bandgap shifts by as much as 40% can be achieved with ˜30 mN of applied magnetic force. This structure has potential for extension in 2D and 3D, providing a general approach for building dynamically tunable elastic metamaterials for applications in lensing and guiding elastic waves.
STIFF: Converting Scientific FITS Images to TIFF
NASA Astrophysics Data System (ADS)
Bertin, Emmanuel
2011-10-01
STIFF is a program that converts scientific FITS1 images to the more popular TIFF2 format for illustration purposes. Most FITS readers and converters do not do a proper job at converting FITS image data to 8 bits. 8-bit images stored in JPEG, PNG or TIFF files have the intensities implicitely stored in a non-linear way. Most current FITS image viewers and converters provide the user an incorrect translation of the FITS image content by simply rescaling linearly input pixel values. A first consequence is that the people working on astronomical images usually have to apply narrow intensity cuts or square-root or logarithmic intensity transformations to actually see something on their deep-sky images. A less obvious consequence is that colors obtained by combining images processed this way are not consistent across such a large range of surface brightnesses. Though with other software the user is generally afforded a choice of nonlinear transformations to apply in order to make the faint stuff stand out more clearly in the images, with the limited selection of choices provides, colors will not be accurately rendered, and some manual tweaking will be necessary. The purpose of STIFF is to produce beautiful pictures in an automatic and consistent way.
NASA Astrophysics Data System (ADS)
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.
Parameter estimation for stiff deterministic dynamical systems via ensemble Kalman filter
NASA Astrophysics Data System (ADS)
Arnold, Andrea; Calvetti, Daniela; Somersalo, Erkki
2014-10-01
A commonly encountered problem in numerous areas of applications is to estimate the unknown coefficients of a dynamical system from direct or indirect observations at discrete times of some of the components of the state vector. A related problem is to estimate unobserved components of the state. An egregious example of such a problem is provided by metabolic models, in which the numerous model parameters and the concentrations of the metabolites in tissue are to be estimated from concentration data in the blood. A popular method for addressing similar questions in stochastic and turbulent dynamics is the ensemble Kalman filter (EnKF), a particle-based filtering method that generalizes classical Kalman filtering. In this work, we adapt the EnKF algorithm for deterministic systems in which the numerical approximation error is interpreted as a stochastic drift with variance based on classical error estimates of numerical integrators. This approach, which is particularly suitable for stiff systems where the stiffness may depend on the parameters, allows us to effectively exploit the parallel nature of particle methods. Moreover, we demonstrate how spatial prior information about the state vector, which helps the stability of the computed solution, can be incorporated into the filter. The viability of the approach is shown by computed examples, including a metabolic system modeling an ischemic episode in skeletal muscle, with a high number of unknown parameters.
Damage detection using experimentally measured mass and stiffness matrices
NASA Technical Reports Server (NTRS)
Peterson, L. D.; Alvin, K. F.; Doebling, S. W.; Park, K. C.
1993-01-01
A method is presented for locating physical damage or change in a structure using experimentally measured mass and stiffness matrices. The approach uses a recently developed algorithm for transforming a state-space realization into a second order structural model with physical displacements as the generalized coordinates. This is accomplished by first rotating a state-space model of the identified structural dynamics into modal coordinates and approximating the mass normalized modal vectors for the output measurement set. Next, the physical mass, damping and stiffness matrices are synthesized directly from the measured modal parameters. This yields experimental mass and stiffness matrices for the structure without the use of a finite element model or a numerical search. The computed mass and stiffness are asymptotically equivalent to a static condensation of the global physical coordinate model. Techniques for solving the inverse connectivity problem are then developed whereby it is possible to assess the stiffness in a region of the structure bounded by several sensors. Applications to both simulated data and experimental data are used to discuss the effectiveness of the approach.
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
Carrier mediated reduction of stiffness in nanoindented crystalline Si(100)
Kataria, S. Dhara, Sandip Dash, S.; Tyagi, A. K.
2015-07-21
We report the observation of carrier mediated decrease in the stiffness of crystalline (c)-Si(100) under nanoindentation. The apparent elastic moduli of heavily doped (∼1 × 10{sup 21} cm{sup −3}) p- and n-type c-Si are observed to be lower by 5.3%–7.5% than the estimated value for intrinsic (∼1 × 10{sup 14} cm{sup −3}) c-Si. The deviation observed with respect to elastic modulus remarkably matches with the estimated value while considering the electronic elastic strain effect on carrier concentration as an influence of negative pressure coefficient of band gap for Si (Γ-X). The value is predominantly higher than the reported value of a decrease of 1%–3% in stiffness as an effect of impurity in c-Si.
Bounding the Bogoliubov coefficients
Boonserm, Petarpa; Visser, Matt
2008-11-15
While over the last century or more considerable effort has been put into the problem of finding approximate solutions for wave equations in general, and quantum mechanical problems in particular, it appears that as yet relatively little work seems to have been put into the complementary problem of establishing rigourous bounds on the exact solutions. We have in mind either bounds on parametric amplification and the related quantum phenomenon of particle production (as encoded in the Bogoliubov coefficients), or bounds on transmission and reflection coefficients. Modifying and streamlining an approach developed by one of the present authors [M. Visser, Phys. Rev. A 59 (1999) 427-438, (arXiv:quant-ph/9901030)], we investigate this question by developing a formal but exact solution for the appropriate second-order linear ODE in terms of a time-ordered exponential of 2x2 matrices, then relating the Bogoliubov coefficients to certain invariants of this matrix. By bounding the matrix in an appropriate manner, we can thereby bound the Bogoliubov coefficients.
Simulation methods with extended stability for stiff biochemical Kinetics
2010-01-01
Background With increasing computer power, simulating the dynamics of complex systems in chemistry and biology is becoming increasingly routine. The modelling of individual reactions in (bio)chemical systems involves a large number of random events that can be simulated by the stochastic simulation algorithm (SSA). The key quantity is the step size, or waiting time, τ, whose value inversely depends on the size of the propensities of the different channel reactions and which needs to be re-evaluated after every firing event. Such a discrete event simulation may be extremely expensive, in particular for stiff systems where τ can be very short due to the fast kinetics of some of the channel reactions. Several alternative methods have been put forward to increase the integration step size. The so-called τ-leap approach takes a larger step size by allowing all the reactions to fire, from a Poisson or Binomial distribution, within that step. Although the expected value for the different species in the reactive system is maintained with respect to more precise methods, the variance at steady state can suffer from large errors as τ grows. Results In this paper we extend Poisson τ-leap methods to a general class of Runge-Kutta (RK) τ-leap methods. We show that with the proper selection of the coefficients, the variance of the extended τ-leap can be well-behaved, leading to significantly larger step sizes. Conclusions The benefit of adapting the extended method to the use of RK frameworks is clear in terms of speed of calculation, as the number of evaluations of the Poisson distribution is still one set per time step, as in the original τ-leap method. The approach paves the way to explore new multiscale methods to simulate (bio)chemical systems. PMID:20701766
Torsional stiffness degradation and aerostatic divergence of suspension bridge decks
NASA Astrophysics Data System (ADS)
Zhang, Z. T.; Ge, Y. J.; Yang, Y. X.
2013-07-01
The mechanism of aerostatic torsional divergence (ATD) of long-span suspension bridges is investigated. A theoretical analysis on the basis of a generalized model is presented, showing that the vertical motion of a bridge deck is crucial to the torsional stiffness of the whole suspended system, and that the vertical motion of either cable with a magnitude beyond a certain threshold could result in a sudden degradation of the torsional stiffness of the system. This vertical motion-induced degradation of stiffness is recognized as the main reason for the ATD. Long-span suspension bridges are susceptible to such a type of divergence, especially when they are immersed in turbulent wind fields. The divergences that occur in turbulent wind fields differ significantly from those in smooth wind fields, and the difference is well explained by the generalized model that the loosening of any one cable could result in the vanishing of the part of stiffness provided by the whole cable system. The mechanism revealed in this paper leads to a definition of the critical wind speed of the ATD in a turbulent flow; that is, the one resulting in a vertical motion so large as to loosen either cable to a stressless state. Numerical results from the nonlinear finite-element (FE) analysis of the Xihoumen suspension bridge, in conjunction with observations from wind tunnel tests on an aero-elastic full bridge model, are in support of the viewpoint presented in this study.
Difference methods for stiff delay differential equations. [DDESUB, in FORTRAN
Roth, Mitchell G.
1980-12-01
Delay differential equations of the form y'(t) = f(y(t), z(t)), where z(t) = (y/sub 1/(..cap alpha../sub 1/(y(t))),..., y/sub n/(..cap alpha../sub n/(y(t))))/sup T/ and ..cap alpha../sub i/(y(t)) less than or equal to t, arise in many scientific and engineering fields when transport lags and propagation times are physically significant in a dynamic process. Difference methods for approximating the solution of stiff delay systems require special stability properties that are generalizations of those employed for stiff ordinary differential equations. By use of the model equation y'(t) = py(t) + qy(t-1), with complex p and q, the definitions of A-stability, A( )-stability, and stiff stability have been generalize to delay equations. For linear multistep difference formulas, these properties extend directly from ordinary to delay equations. This straight forward extension is not true for implicit Runge-Kutta methods, as illustrated by the midpoint formula, which is A-stable for ordinary equations, but not for delay equations. A computer code for stiff delay equations was developed using the BDF. 24 figures, 5 tables.
Experimental study of the Biot coefficient of Bakken cores
NASA Astrophysics Data System (ADS)
Ma, X.; Zoback, M. D.
2015-12-01
We have performed a series of exhaustive experiments to measure the Biot coefficient (α) of the tight cores from the Bakken shale oil play. Five distinct, bedding-normal cores from a vertical well were tested, covering the sequences of Three Forks, Lower, Middle, and Upper Bakken, and Lodgepole. The scope of this laboratory study is two-fold: (1) to obtain realistic Biot coefficient for modeling reservoir stress changes due to depletion and injection; (2) to characterize the poromechanical properties in relation to rock's mineral composition and microstructure. The experiments were carried out as follows: Argon-saturated specimen (1-inch length, 1-inch diameter) was subjected to hydrostatic confining pressure under drained conditions. Pore pressure was regulated as Argon was injected into both ends of the specimen. We drilled multiple non-through-going boreholes (1-mm diameter) in the specimen to facilitate pressure equilibrium, without compromising its integrity. The specimen was put through a loading path to experience confining pressure and pore pressure up to 70 and 60 MPa, respectively. Axial and lateral strains were recorded and used to calculate the rock's bulk stiffness, and subsequently the static Biot coefficient, which is related to reservoir deformation and associated stress changes. Results of all five cores unanimously show that α is less than unity and is a function of both confining and pore pressure. α generally varies between 0.3 and 0.9 for the pressure levels we applied. This implies that models of reservoir deformation and its stress change using Terzaghi's simple effective stress law (α = 1) or a constant α less than 1 may be erroneous. Typically, α rises significantly with pore pressure, but declines with confining pressure to the degree that is dependent on rock's bulk stiffness. We found the stiffness of these rocks does not correlate well with the content of compliant components (e.g., clay and kerogen), and the drastic difference in
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
Experimental stiffness of tapered bore seals
NASA Technical Reports Server (NTRS)
Fleming, D. P.
1985-01-01
The stiffness of tapered-bore ring seals was measured with air as the sealed fluid. Static stiffness agreed fairly well with results of a previous analysis. Cross-coupled stiffness due to shaft rotation was much less than predicted. It is suggested that part of the disparity may be due to simplifying assumptions in the analysis; however, these do not appear to account for the entire difference observed.
Validity and reliability of clinical tests for assessing hip passive stiffness.
Carvalhais, Viviane Otoni do Carmo; de Araújo, Vanessa Lara; Souza, Thales Rezende; Gonçalves, Gabriela Gomes Pavan; Ocarino, Juliana de Melo; Fonseca, Sérgio Teixeira
2011-06-01
Inadequate levels of hip passive joint stiffness have been associated with the occurrence of movement dysfunction, development of pathologies and reduction in performance. Clinical tests, designed to evaluate hip joint stiffness, may allow the identification of improper stiffness levels. The purpose of this study was to determine the concurrent validity as well as the intra- and inter-examiners reliabilities of clinical measures used to assess hip passive stiffness during internal rotation. Fifteen healthy participants were subjected to test-retest evaluations by two examiners. Two clinical measures were performed: 'position of first detectable resistance' and 'change in passive resistance torque'. The results of these tests were compared to the passive stiffness measured with an isokinetic dynamometer (gold standard measure). A significant correlation was found between the stiffness measured with the isokinetic dynamometer and the clinical measures of 'position of first detectable resistance' (r=-0.85 to -0.86, p<0.001) and 'change in passive resistance torque' (r=0.78 to 0.84, p≤0.001). The Intraclass Correlation Coefficients for intra- and inter-examiners reliabilities varied from 0.95 to 0.99. Thus, the results demonstrated that the clinical measures have adequate validity and reliability for obtaining information on hip passive stiffness during internal rotation. PMID:21212014
NASA Astrophysics Data System (ADS)
Wang, Lijin
2016-06-01
The stochastic protein kinetic equations can be stiff for certain parameters, which makes their numerical simulation rely on very small time step sizes, resulting in large computational cost and accumulated round-off errors. For such situation, we provide a method of reducing stiffness of the stochastic protein kinetic equation by means of a kind of variable transformation. Theoretical and numerical analysis show effectiveness of this method. Its generalization to a more general class of stochastic differential equation models is also discussed.
Arthroscopic Treatment of Stiff Elbow
Blonna, Davide; Bellato, Enrico; Marini, Eleonora; Scelsi, Michele; Castoldi, Filippo
2011-01-01
Contracture of the elbow represents a disabling condition that can impair a person's quality of life. Regardless of the event that causes an elbow contracture, the conservative or surgical treatment is usually considered technically difficult and associated with complications. When the conservative treatment fails to restore an acceptable range of motion in the elbow, open techniques have been shown to be successful options. More recently the use of arthroscopy has become more popular for several reasons. These reasons include better visualization of intra-articular structures, less tissue trauma from open incisions, and potentially the ability to begin early postoperative motion. The purpose of this paper is to review the indications, complications, and results of arthroscopic management of a stiff elbow. PMID:22084755
NASA Astrophysics Data System (ADS)
Español, P.; de la Torre, J. A.; Ferrario, M.; Ciccotti, G.
2011-11-01
The method of constraints in molecular dynamics is useful because it avoids the resolution of high frequency motions with very small time steps. However, the price to pay is that both the dynamics and the statistics of a constrained system differ from those of the unconstrained one. Instead of using constraints, we propose to dispose of high frequency motions by a coarse-graining procedure in which fast variables are eliminated. These fast variables are thus modeled as friction and thermal fluctuations. We illustrate the methodology with a simple model case, a diatomic molecule in a monoatomic solvent, in which the bond between the atoms of a diatomic molecule is stiff. Although the example is very simple and does not display the interesting effects of "wrong" statistics of the constrained system (i.e. the well-known issue connected to the Fixman potential), it is well suited to give the proof of concept of the whole procedure.
Esquivel, Amanda O.; Duncan, Douglas D.; Dobrasevic, Nikola; Marsh, Stephanie M.; Lemos, Stephen E.
2015-01-01
Background: Rotator cuff tendinopathy is a frequent cause of shoulder pain that can lead to decreased strength and range of motion. Failures after using the single-row technique of rotator cuff repair have led to the development of the double-row technique, which is said to allow for more anatomical restoration of the footprint. Purpose: To compare 5 different types of suture patterns while maintaining equality in number of anchors. The hypothesis was that the Mason-Allen–crossed cruciform transosseous-equivalent technique is superior to other suture configurations while maintaining equality in suture limbs and anchors. Study Design: Controlled laboratory study. Methods: A total of 25 fresh-frozen cadaveric shoulders were randomized into 5 suture configuration groups: single-row repair with simple stitch technique; single-row repair with modified Mason-Allen technique; double-row Mason-Allen technique; double-row cross-bridge technique; and double-row suture bridge technique. Load and displacement were recorded at 100 Hz until failure. Stiffness and bone mineral density were also measured. Results: There was no significant difference in peak load at failure, stiffness, maximum displacement at failure, or mean bone mineral density among the 5 suture configuration groups (P < .05). Conclusion: According to study results, when choosing a repair technique, other factors such as number of sutures in the repair should be considered to judge the strength of the repair. Clinical Relevance: Previous in vitro studies have shown the double-row rotator cuff repair to be superior to the single-row repair; however, clinical research does not necessarily support this. This study found no difference when comparing 5 different repair methods, supporting research that suggests the number of sutures and not the pattern can affect biomechanical properties. PMID:26665053
Medial-Lateral Postural Control in Older Adults Exhibits Increased Stiffness and Damping
Cenciarini, Massimo; Loughlin, Patrick J.; Sparto, Patrick J.; Redfern, Mark S.
2016-01-01
Older adults often exhibit increased co-contraction in response to a balance perturbation. This response is generally thought to enhance stability by increasing joint stiffness. We investigated the issue of increased stiffness in postural control by exposing seven older (75 ±5 y) and ten young (24 ± 3 y) adults to pseudo-random medial-lateral (ML) floor tilts, and then fitting the measured ML body sway data to a previously-developed postural control model that includes stiffness and damping parameters. Significant increases were found in both parameters in the older adults compared to the young adults. This concurrent increase in stiffness and damping is more stabilizing than an increase in stiffness alone, which can lead to resonances. PMID:19964728
A novel assessment technique for measuring ankle orientation and stiffness.
Zhang, Mingming; Davies, T Claire; Nandakumar, Anoop; Quan Xie, Sheng
2015-09-18
The measurement of ankle orientation and stiffness can provide insight into improvements and allows for effective monitoring during a rehabilitation program. Existing assessment techniques have a variety of limitations. Dynamometer based methods rely on manual manipulation. The use of torque meter is usually for single degree-of-freedom (DOF) devices. This study proposes a novel ankle assessment technique that can be used for multiple DOFs devices working in both manual and automatic modes using the position sensor and the multi-axis load cell. As a preliminary evaluation, an assessment device for ankle dorsiflexion and plantarflexion was constructed. Nine subjects participated to evaluate the effectiveness of the assessment device in determining ankle orientation and stiffness. The measured ankle orientation was consistent with that from the NDI Polaris optical tracking system. The measured ankle torque and stiffness compared well with published data. The test-retest reliability was high with intraclass correlation coefficient (ICC2, 1) values greater than 0.846 and standard error of measurement (SEM) less than 1.38. PMID:26159061
Multi-flexible-body dynamics capturing motion-induced stiffness
NASA Technical Reports Server (NTRS)
Banerjee, Arun K.; Lemak, Mark E.; Dickens, John M.
1989-01-01
A multi-flexible-body dynamics formulation incorporating a recently developed theory for capturing motion induced stiffness for a arbitrary structure undergoing large rotation and translation accompanied by small vibrations is presented. In essence, the method consists of correcting prematurely linearized dynamical equations for an arbitrary flexible body with generalized active forces due to geometric stiffness corresponding to a system of twelve inertia forces and nine inertia couples distributed over the body. Equations of motion are derived by means of Kane's method. A useful feature of the formulation is its treatment of prescribed motions and interaction forces. Results of simulations of motions of three flexible spacecraft, involving stiffening during spinup motion, dynamic buckling, and a repositioning maneuver, demonstrate the validity and generality of the theory.
Nonparticipatory Stiffness in the Male Perioral Complex
ERIC Educational Resources Information Center
Chu, Shin-Ying; Barlow, Steven M.; Lee, Jaehoon
2009-01-01
Purpose: The objective of this study was to extend previous published findings in the authors' laboratory using a new automated technology to quantitatively characterize nonparticipatory perioral stiffness in healthy male adults. Method: Quantitative measures of perioral stiffness were sampled during a nonparticipatory task using a…
Relative stiffness of flat-conductor cable
NASA Technical Reports Server (NTRS)
Hankins, J. D.
1977-01-01
Bending moment data were taken on ten different cable samples and normalized to express all stiffness factors in terms of cable 5.1 cm in width. Relative stiffness data and nominal physical characteristics are tabulated and presented in graphical form for designers who may be interested in finding torques exerted on critical components by short lengths of cable.
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.
The posttraumatic stiff elbow: an update.
Mellema, Jos J; Lindenhovius, Anneluuk L C; Jupiter, Jesse B
2016-06-01
Posttraumatic elbow stiffness is a disabling condition that remains challenging to treat despite improvement of our understanding of the pathogenesis of posttraumatic contractures and new treatment regimens. This review provides an update and overview of the etiology of posttraumatic elbow stiffness, its classification, evaluation, nonoperative and operative treatment, and postoperative management. PMID:26984466
Negative-stiffness-mechanism vibration isolation systems
NASA Astrophysics Data System (ADS)
Platus, David L.
1992-02-01
A new type of vibration isolation system offers significant improvement in performance compared with current state-of-the-art systems. The system uses negative-stiffness mechanisms to cancel the stiffness of a spring suspension. Reduction in stiffness magnifies the damping inherent in the system creating a practical means for achieving high hysteretic damping. The result is a simple, compact 6-DOF passive isolation system capable of system resonant frequencies below 0.2 Hz and first isolator resonances above 100 Hz. Resonant transmissibilities below 1.4 can be achieved with transmissibilities at the higher frequencies close to that of the ideal undamped system. The negative-stiffness mechanisms can cancel the stiffness of power cables, hoses or other lines connected to payloads. This paper develops the theory, describes typical configurations and summarizes test data with prototype systems.
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.
NASA Astrophysics Data System (ADS)
CHU, F.; LU, W.
2001-11-01
The rotor-to-stator rub is one of the main serious malfunctions that often occur in rotating machinery. Previous research has provided enough tools to judge the existence of this fault. However, it is still a difficult task to detect the rubbing position in a multi-disk rotor system. In this paper, the stiffness is considered as variable and the rub-impact effect is included in this dynamic stiffness. Based on simulation data the least-square method is used to identify the dynamic stiffness at different positions along the rotor. It is found that the dynamic stiffness at the position where the rub-impact occurs is increasing as the rubbing develops and this stiffness at other positions shows very little change. The damping coefficients have similar trends. This method is found to be very effective in detecting the rubbing position.
Wave Propagation of Myocardial Stretch: Correlation with Myocardial Stiffness
Pislaru, Cristina; Pellikka, Patricia A.; Pislaru, Sorin V.
2015-01-01
The mechanism of flow propagation during diastole in the left ventricle (LV) has been well described. Little is known about the associated waves propagating along the heart wall s. These waves may have a mechanism similar to pulse wave propagation in arteries. The major goal of the study was to evaluate the effect of myocardial stiffness and preload on this wave transmission. Methods Longitudinal late diastolic deformation and wave speed (Vp) of myocardial stretch in the anterior LV wall were measured using sonomicrometry in sixteen pigs. Animals with normal and altered myocardial stiffness (acute myocardial infarction) were studied with and without preload alterations. Elastic modulus estimated from Vp (EVP; Moens-Korteweg equation) was compared to incremental elastic modulus obtained from exponential end -diastolic stress-strain relation (ESS). Myocardial distensibility and α-and β-coefficients of stress-strain relations were calculated. Results Vp was higher at reperfusion compared to baseline (2.6±1.3 m/s vs. 1.3±0.4 m/s; p=0.005) and best correlated with ESS (r 2=0.80, p<0.0001), β-coefficient (r2=0.78, p<0.0001), distensibility (r2=0.47, p=0.005), and wall thickness/diameter ratio (r2=0.42, p=0.009). Elastic moduli (EVP and ESS) were strongly correlated (r2=0.83, p<0.0001). Increasing preload increased Vp and EVP and decreased distensibility. At multivariate analysis, ESS, wall thickness, and end-diastolic and systolic LV pressures were independent predictors of Vp (r2model=0.83, p<0.0001). Conclusions The main determinants of wave propagation of longitudinal myocardial stretch were myocardial stiffness and LV geometry and pressure. This local wave speed could potentially be measured noninvasively by echocardiography. PMID:25193091
High performance composites with active stiffness control.
Tridech, Charnwit; Maples, Henry A; Robinson, Paul; Bismarck, Alexander
2013-09-25
High performance carbon fiber reinforced composites with controllable stiffness could revolutionize the use of composite materials in structural applications. Here we describe a structural material, which has a stiffness that can be actively controlled on demand. Such a material could have applications in morphing wings or deployable structures. A carbon fiber reinforced-epoxy composite is described that can undergo an 88% reduction in flexural stiffness at elevated temperatures and fully recover when cooled, with no discernible damage or loss in properties. Once the stiffness has been reduced, the required deformations can be achieved at much lower actuation forces. For this proof-of-concept study a thin polyacrylamide (PAAm) layer was electrocoated onto carbon fibers that were then embedded into an epoxy matrix via resin infusion. Heating the PAAm coating above its glass transition temperature caused it to soften and allowed the fibers to slide within the matrix. To produce the stiffness change the carbon fibers were used as resistance heating elements by passing a current through them. When the PAAm coating had softened, the ability of the interphase to transfer load to the fibers was significantly reduced, greatly lowering the flexural stiffness of the composite. By changing the moisture content in PAAm fiber coating, the temperature at which the PAAm softens and the composites undergo a reduction in stiffness can be tuned. PMID:23978266
Dynamic stiffness formulation for free orthotropic plates
NASA Astrophysics Data System (ADS)
Ghorbel, O.; Casimir, J. B.; Hammami, L.; Tawfiq, I.; Haddar, M.
2015-06-01
This paper presents a procedure for developing the dynamic stiffness matrix of a free orthotropic Kirchhoff plate. The dynamic stiffness matrix is computed for free edge boundary conditions of the plate that allow assembly procedures. The method is based on a strong formulation of Kirchhoff plate equations and series solutions, taking advantage of the symmetry and Gorman type decomposition of the free boundary conditions. The performances of the so-called Dynamic Stiffness Method (DSM) are evaluated by comparing the harmonic responses of an orthotropic Kirchhoff plate with those obtained from the Finite Element Method using four noded quadrilateral elements.
Materials analogue of zero-stiffness structures
NASA Astrophysics Data System (ADS)
Kumar, Arun; Subramaniam, Anandh
2011-04-01
Anglepoise lamps and certain tensegrities are examples of zero-stiffness structures. These structures are in a state of neutral equilibrium with respect to changes in configuration of the system. Using Eshelby's example of an edge dislocation in a thin plate that can bend, we report the discovery of a non-trivial new class of material structures as an analogue to zero-stiffness structures. For extended positions of the edge dislocation in these structures, the dislocation experiences a zero image force. Salient features of these material structures along with the key differences from conventional zero-stiffness structures are pointed out.
Effects of antihypertensive drugs on arterial stiffness.
Dudenbostel, Tanja; Glasser, Stephen P
2012-01-01
In this review, we discuss the possible pathophysiological mechanisms and the role of arterial stiffness as a biomarker, a blood pressure-independent predictor of cardiovascular morbidity and mortality. The effects of different antihypertensive drug classes on noninvasively assessed markers of arterial stiffness are also discussed. Current evidence will be reviewed regarding the effect of drugs on arterial stiffness, including the peripheral and central effects of angiotensin-converting enzyme inhibitors, angiotensin receptor antagonists, dihydropyridine calcium channel blockers, beta blockers (including vasodilating beta blockers), diuretics, and mineralocorticoid antagonists. PMID:22573107
Physiotherapy assessment of shoulder stiffness and how it influences management
Russell, Sarah
2015-01-01
Common causes of shoulder stiffness include osteoarthritis, trauma, rheumatological conditions and stiffness secondary to soft tissue adaptation. Physiotherapy assessment of the stiff shoulder aims to ascertain the key causative factors of stiffness to inform effective management planning. Identification of whether a patient presents with pain or stiffness as their predominant symptom further guides treatment selection. The current evidence base underpins a management algorithm which has been developed to guide the assessment and management of patients presenting with shoulder stiffness.
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
“Smooth Muscle Cell Stiffness Syndrome”—Revisiting the Structural Basis of Arterial Stiffness
Sehgel, Nancy L.; Vatner, Stephen F.; Meininger, Gerald A.
2015-01-01
In recent decades, the pervasiveness of increased arterial stiffness in patients with cardiovascular disease has become increasingly apparent. Though, this phenomenon has been well documented in humans and animal models of disease for well over a century, there has been surprisingly limited development in a deeper mechanistic understanding of arterial stiffness. Much of the historical literature has focused on changes in extracellular matrix proteins—collagen and elastin. However, extracellular matrix changes alone appear insufficient to consistently account for observed changes in vascular stiffness, which we observed in our studies of aortic stiffness in aging monkeys. This led us to examine novel mechanisms operating at the level of the vascular smooth muscle cell (VSMC)—that include increased cell stiffness and adhesion to extracellular matrix—which that may be interrelated with other mechanisms contributing to arterial stiffness. We introduce these observations as a new concept—the Smooth Muscle Cell Stiffness Syndrome (SMCSS)—within the field of arterial stiffness and posit that stiffening of vascular cells impairs vascular function and may contribute stiffening to the vasculature with aging and cardiovascular disease. Importantly, this review article revisits the structural basis of arterial stiffness in light of these novel findings. Such classification of SMCSS and its contextualization into our current understanding of vascular mechanics may be useful in the development of strategic therapeutics to directly target arterial stiffness. PMID:26635621
Factor Scores, Structure Coefficients, and Communality Coefficients
ERIC Educational Resources Information Center
Goodwyn, Fara
2012-01-01
This paper presents heuristic explanations of factor scores, structure coefficients, and communality coefficients. Common misconceptions regarding these topics are clarified. In addition, (a) the regression (b) Bartlett, (c) Anderson-Rubin, and (d) Thompson methods for calculating factor scores are reviewed. Syntax necessary to execute all four…
Calculation of the lateral control of swept and unswept flexible wings of arbitrary stiffness
NASA Technical Reports Server (NTRS)
Diederich, Franklin W
1951-01-01
A method similar to that of NACA rep. 1000 is presented for calculating the effectiveness and the reversal speed of lateral-control devices on swept and unswept wings of arbitrary stiffness. Provision is made for using either stiffness curves and root-rotation constants or structural influence coefficients in the analysis. Computing forms and an illustrative example are included to facilitate calculations by means of the method. The effectiveness of conventional aileron configurations and the margin against aileron reversal are shown to be relatively low for swept wings at all speeds and for all wing plan forms at supersonic speeds.
Programmable variable stiffness 2D surface design
NASA Astrophysics Data System (ADS)
Trabia, Sarah; Hwang, Taeseon; Yim, Woosoon
2014-03-01
Variable stiffness features can contribute to many engineering applications ranging from robotic joints to shock and vibration mitigation. In addition, variable stiffness can be used in the tactile feedback to provide the sense of touch to the user. A key component in the proposed device is the Biased Magnetorheological Elastomer (B-MRE) where iron particles within the elastomer compound develop a dipole interaction energy. A novel feature of this device is to introduce a field induced shear modulus bias via a permanent magnet which provides an offset with a current input to the electromagnetic control coil to change the compliance or modulus of a base elastomer in both directions (softer or harder). The B-MRE units can lead to the design of a variable stiffness surface. In this preliminary work, both computational and experimental results of the B-MRE are presented along with a preliminary design of the programmable variable stiffness surface design.
Vascular stiffness in insulin resistance and obesity
Jia, Guanghong; Aroor, Annayya R.; DeMarco, Vincent G.; Martinez-Lemus, Luis A.; Meininger, Gerald A.; Sowers, James R.
2015-01-01
Obesity, insulin resistance, and type 2 diabetes are associated with a substantially increased prevalence of vascular fibrosis and stiffness, with attendant increased risk of cardiovascular and chronic kidney disease. Although the underlying mechanisms and mediators of vascular stiffness are not well understood, accumulating evidence supports the role of metabolic and immune dysregulation related to increased adiposity, activation of the renin angiotensin aldosterone system, reduced bioavailable nitric oxide, increased vascular extracellular matrix (ECM) and ECM remodeling in the pathogenesis of vascular stiffness. This review will give a brief overview of the relationship between obesity, insulin resistance and increased vascular stiffness to provide a contemporary understanding of the proposed underlying mechanisms and potential therapeutic strategies. PMID:26321962
An analysis of traction drive torsional stiffness
NASA Technical Reports Server (NTRS)
Rohn, D. A.; Loewenthal, S. H.
1983-01-01
The tangential compliance of elastic bodies in concentrated contact applied to traction drive elements to determine their torsional stiffness was analyzed. Static loading and rotating conditions are considered. The effects of several design variables are shown. The theoretical torsional stiffness of a fixed ratio multiroller drive is computed and compared to experimental values. It is shown that the torsional compliance of the traction contacts themselves is a relatively small portion of the overall drive system compliance.
Dynamic influences of changing gear tooth stiffness
Morguel, O.K.; Esat, I.
1997-07-01
One of the principal sources of vibratory excitation of gear a system is due to the angular speed fluctuation of meshing gears due to non-linearities and profile errors and tooth and supporting bearings flexibility. The transmission error is also influenced by the varying force at the contact point of the meshing gear teeth. The varying contact force itself is influenced by the varying tooth stiffness due to change of orientation of teeth relative to each other, during the contact phase of each pair. This paper presents a simplified single degree of freedom gear system. It is assumed that one member of the gear pair is rigid and flexibility of the gear tooth is attributed only to one section of the gear system. This enables the equation to be simplified to a single degree of freedom system. The resulting non-linear equation is solved iteratively by employing a method which combines piecewise linearization for the stiffness and resulting contact orientation shift due to shaft and tooth flexibility. The contact shift will be referred as the phase shift in this report. The early finding indicates that there are significant differences between the response of the system incorporating three different tooth stiffness, namely, constant tooth stiffness, rectangular wave tooth stiffness and sinusoidal tooth stiffness. The results also implies that any design specification associated with gears has to include gear tooth influences, especially if the excitation is of a major concern. The rectangular stiffness variation which most accurately describes the tooth stiffness gives a response fluctuation, studied in the frequency domain shows that the effective natural frequencies fluctuates between certain upper and lower limits. Thus the paper suggest that any design study should consider these limits.
Stiffness and Confinement Ratios of SMA Wire Jackets for Confining Concrete
NASA Astrophysics Data System (ADS)
Choi, Eunsoo; Kim, Dong Joo; Youn, Heejung
2014-07-01
This article discusses the effects of the stiffness and confinement ratios of shape memory alloy (SMA) wire jackets on the behavior of confined concrete. SMA wire jackets are an effective confining material to improve concrete behavior; for example, by increasing peak strength and failure strain. The stiffness and confinement ratios of fiber-reinforced polymer jackets have been extensively discussed and their effects are well known. However, assessment of the stiffness and confinement ratios of SMA wire jackets has not previously been conducted. In this study, we investigate the effects of the stiffness and confinement ratios of steel jackets, and then compare the results with those of SMA wire jackets. In general, the stiffness ratios of SMA wire jackets are relatively smaller than those of steel jackets, and most of them have lower stiffness ratios because the Young's moduli of the SMAs are relatively small. The active confining pressure of the SMA wires does not improve the lower stiffness-ratio effect since the amount of active confining pressure is not sufficiently large.
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.
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 (ΔF) and interangle span (ΔX), 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 of Railway Soil-Steel Structures
NASA Astrophysics Data System (ADS)
Machelski, Czesław
2015-12-01
The considerable influence of the soil backfill properties and that of the method of compacting it on the stiffness of soil-steel structures is characteristic of the latter. The above factors (exhibiting randomness) become apparent in shell deformation measurements conducted during construction and proof test loading. A definition of soil-shell structure stiffness, calculated on the basis of shell deflection under the service load, is proposed in the paper. It is demonstrated that the stiffness is the inverse of the deflection influence function used in structural mechanics. The moving load methodology is shown to be useful for testing, since it makes it possible to map the shell deflection influence line also in the case of group loads (concentrated forces), as in bridges. The analyzed cases show that the shell's span, geometry (static scheme) and the height of earth fill influence the stiffness of the structure. The soil-steel structure's characteristic parameter in the form of stiffness k is more suitable for assessing the quality of construction works than the proposed in code geometric index ω applied to beam structures. As shown in the given examples, parameter k is more effective than stiffness parameter λ used to estimate the deformation of soil-steel structures under construction. Although the examples concern railway structures, the methodology proposed in the paper is suitable also for road bridges.
Stiff limb syndrome: a case report
2010-01-01
Introduction Stiff limb syndrome is a clinical feature of the stiff person syndrome, which is a rare and disabling neurologic disorder characterized by muscle rigidity and episodic spasms that involve axial and limb musculature. It is an autoimmune disorder resulting in a malfunction of aminobutyric acid mediated inhibitory networks in the central nervous system. We describe a patient diagnosed by neurological symptoms of stiff limb syndrome with a good outcome after treatment, and a review of the related literature. Case presentation A 49-year-old male patient presented with a progressive stiffness and painful spasms of his both legs resulting in a difficulty of standing up and walking. The diagnosis of stiff limb syndrome was supported by the dramatically positive response to treatment using diazepam 25 mg/day and baclofen 30 mg/day. Conclusion This clinical case highlights the importance of a therapeutic test to confirm the diagnosis of stiff limb syndrome especially when there is a high clinical suspicion with unremarkable electromyography PMID:20205913
Longitudinal relaxation of initially straight flexible and stiff polymers
NASA Astrophysics Data System (ADS)
Dimitrakopoulos, Panagiotis; Dissanayake, Inuka
2004-11-01
The present talk considers the relaxation of a single flexible or stiff polymer chain from an initial straight configuration in a viscous solvent. This problem commonly arises when strong flows are turned off in both industrial and biological applications. The problem is also motivated by recent experiments with single biopolymer molecules relaxing after being fully extended by applied forces as well as by the recent development of micro-devices involving stretched tethered biopolymers. Our results are applicable to a wide array of synthetic polymers such as polyacrylamides, Kevlar and polyesters as well as biopolymers such as DNA, actin filaments, microtubules and MTV. In this talk we discuss the mechanism of the polymer relaxation as was revealed through Brownian Dynamics simulations covering a broad range of time scales and chain stiffness. After the short-time free diffusion, the chain's longitudinal reduction at early intermediate times is shown to constitute a universal behavior for any chain stiffness caused by a quasi-steady relaxation of tensions associated with the deforming action of the Brownian forces. Stiff chains are shown to exhibit a late intermediate-time longitudinal reduction associated with a relaxation of tensions affected by the deforming Brownian and the restoring bending forces. The longitudinal and transverse relaxations are shown to obey different laws, i.e. the chain relaxation is anisotropic at all times. In the talk, we show how from the knowledge of the relaxation mechanism, we can predict and explain the polymer properties including the polymer stress and the solution birefringence. In addition, a generalized stress-optic law is derived valid for any time and chain stiffness. All polymer properties which depend on the polymer length are shown to exhibit two intermediate-time behaviors with the early one to constitute a universal behavior for any chain stiffness. This work was supported in part by the Minta Martin Research Fund. The
Estimating the Polyserial Correlation Coefficient.
ERIC Educational Resources Information Center
Bedrick, Edward J.; Breslin, Frederick C.
1996-01-01
Simple noniterative estimators of the polyserial correlation coefficient are developed by exploiting a general relationship between the polyserial correlation and the point polyserial correlation to give extensions of the biserial estimators of K. Pearson (1909), H. E. Brogden (1949), and F. M. Lord (1963) to the multicategory setting. (SLD)
Design of a variable-stiffness robotic hand using pneumatic soft rubber actuators
NASA Astrophysics Data System (ADS)
Nagase, Jun-ya; Wakimoto, Shuichi; Satoh, Toshiyuki; Saga, Norihiko; Suzumori, Koichi
2011-10-01
In recent years, Japanese society has been ageing, engendering a labor shortage of young workers. Robots are therefore expected to be useful in performing tasks such as day-to-day support for elderly people. In particular, robots that are intended for use in the field of medical care and welfare are expected to be safe when operating in a human environment because they often come into contact with people. Furthermore, robots must perform various tasks such as regrasping, grasping of soft objects, and tasks using frictional force. Given these demands and circumstances, a tendon-driven robot hand with a stiffness changing finger has been developed. The finger surface stiffness can be altered by adjusting the input pressure depending on the task. Additionally, the coefficient of static friction can be altered by changing the surface stiffness merely by adjusting the input air pressure. This report describes the basic structure, driving mechanism, and basic properties of the proposed robot hand.
A unit-cell model of textile composite beams for predicting stiffness properties
NASA Technical Reports Server (NTRS)
Sankar, Bhavani V.; Marrey, Ramesh V.
1993-01-01
Flexural stiffness properties of a textile composite beam are obtained from a finite-element model of the unit cell. Three linearly independent deformations, namely, pure extension, pure bending and pure shear, are applied to the unit cell. The top and bottom surfaces of the beam are assumed to be traction free. Periodic boundary conditions on the lateral boundaries of the unit cell are enforced by multi-point constraint elements. From the forces acting on the unit cell, the flexural stiffness coefficients of the composite beam are obtained. The difficulties in determining the transverse shear stiffness are discussed, and a modified approach is presented. The methods are first verified by applying them to isotropic and bimaterial beams for which the results are known, and then illustrated for a simple plain-weave textile composite.
Effect of chain stiffness on interfacial slip in nanoscale polymer films
NASA Astrophysics Data System (ADS)
Priezjev, Nikolai
2013-11-01
The results obtained from molecular dynamics simulations of the friction at an interface between polymer melts and weakly attractive crystalline surfaces are reported. We consider a coarse-grained bead-spring model of linear chains with adjustable intrinsic stiffness. The structure and relaxation dynamics of polymer chains near interfaces are quantified by the radius of gyration and decay of the time autocorrelation function of the first normal mode. We found that the friction coefficient at small slip velocities exhibits a distinct maximum which appears due to shear-induced alignment of semiflexible chain segments in contact with solid walls. At large slip velocities, the friction coefficient is independent of the chain stiffness. The data for the friction coefficient and shear viscosity are used to elucidate main trends in the nonlinear shear rate dependence of the slip length. The influence of chain stiffness on the relationship between the friction coefficient and the structure factor in the first fluid layer is discussed. Financial support from the National Science Foundation (CBET-1033662) is gratefully acknowledged.
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.
Coefficients for Interrater Agreement.
ERIC Educational Resources Information Center
Zegers, Frits E.
1991-01-01
The degree of agreement between two raters rating several objects for a single characteristic can be expressed through an association coefficient, such as the Pearson product-moment correlation. How to select an appropriate association coefficient, and the desirable properties and uses of a class of such coefficients--the Euclidean…
Post-traumatic elbow rotational stiffness
Ling, Samuel KK; Faan, Yan Sui; Lui, Paulina WY; Ngai, Wai Kit
2014-01-01
Background The elbow is an important but complex structure, with movement in both the sagittal plane in flexion and extension, as well as the rotational plane in forearm supination and pronation. Trauma is a common cause of elbow stiffness, which significantly hampers daily function. There are currently no gold-standard management guidelines for post-traumatic elbow stiffness, and most of the published literature focuses solely on the sagittal plane of motion. Methods This is a retrospective case series reviewing all patients who underwent a surgical release for treatment of post-traumatic elbow stiffness during a 36-month period. Motion range and the shortened version of the Disabilities of the Arm, Shoulder and Hand scores were serially measured and analyzed. Results The results obtained showed that both the sagittal and rotational range of motion directly influenced upper limb function; however, the relationship between these two motion planes was weak, meaning that both sagittal and rotational motion in the elbow need be addressed individually. Post-traumatic elbow stiffness could be aptly managed by various surgical approaches, including arthroscopic-assisted procedures; these were all effective in increasing both the sagittal and rotational range of motion. More importantly, this gain in range translated to a statistically significant improvement in upper limb function. Conclusions Management of elbow stiffness needs to be tackled in both the sagittal and rotational motion planes.
Assessments of endothelial function and arterial stiffness are reproducible in patients with COPD
Rodriguez-Miguelez, Paula; Seigler, Nichole; Bass, Leon; Dillard, Thomas A; Harris, Ryan A
2015-01-01
Background Elevated cardiovascular disease risk is observed in patients with COPD. Non-invasive assessments of endothelial dysfunction and arterial stiffness have recently emerged to provide mechanistic insight into cardiovascular disease risk in COPD; however, the reproducibility of endothelial function and arterial stiffness has yet to be investigated in this patient population. Objectives This study sought to examine the within-day and between-day reproducibility of endothelial function and arterial stiffness in patients with COPD. Methods Baseline diameter, peak diameter, flow-mediated dilation, augmentation index, augmentation index at 75 beats per minute, and pulse wave velocity were assessed three times in 17 patients with COPD (six males, eleven females, age range 47–75 years old; forced expiratory volume in 1 second =51.5% predicted). Session A and B were separated by 3 hours (within-day), whereas session C was conducted at least 7 days following session B (between-day). Reproducibility was assessed by: 1) paired t-tests, 2) coefficients of variation, 3) coefficients of variation prime, 4) intra-class correlation coefficient, 5) Pearson’s correlations (r), and 6) Bland–Altman plots. Five acceptable assessments were required to confirm reproducibility. Results Six out of six within-day criteria were met for endothelial function and arterial stiffness outcomes. Six out of six between-day criteria were met for baseline and peak diameter, augmentation index and pulse wave velocity, whereas five out of six criteria were met for flow-mediated dilation. Conclusion The present study provides evidence for within-day and between-day reproducibility of endothelial function and arterial stiffness in patients with COPD. PMID:26396509
Hyper-damping properties of a stiff and stable linear oscillator with a negative stiffness element
NASA Astrophysics Data System (ADS)
Antoniadis, I.; Chronopoulos, D.; Spitas, V.; Koulocheris, D.
2015-06-01
A simple, stiff, statically and dynamically stable linear oscillator incorporating a negative stiffness element is used as a template to provide a generic theoretical basis for a novel vibration damping and isolation concept. This oscillator is designed to present the same overall static stiffness, the same mass and to use the same damping element as a reference classical linear SDoF oscillator. Thus, no increase of the structure mass or the viscous damping is needed, as in the case of a traditional linear isolator, no decrease of the overall structure stiffness is required as in the case of 'zero-stiffness' oscillators with embedded negative stiffness elements. The difference from these two templates consists entirely in the proper redistribution and reallocation of the stiffness and the damping elements of the system. Once such an oscillator is optimally designed, it is shown to exhibit an extraordinary apparent damping ratio, which is even several orders of magnitude higher than that of the original SDoF system, especially in cases where the original damping of the SDoF system is extremely low. This extraordinary damping behavior is a result of the phase difference between the positive and the negative stiffness elastic forces, which is in turn a consequence of the proper redistribution of the stiffness and the damping elements. This fact ensures that an adequate level of elastic forces exists throughout the entire frequency range, able to counteract the inertial and the excitation forces. Consequently, a resonance phenomenon, which is inherent in the original linear SDoF system, cannot emerge in the proposed oscillator. The optimal parameter selection for the design of the negative stiffness oscillator is discussed. To further exhibit the advantages that such a design can generate, the suggested oscillator is implemented within a periodic acoustic metamaterial structure, inducing a radical increase in the damping of the propagating acoustic waves. The concept
Quantitative Elastography for Cervical Stiffness Assessment during Pregnancy
Fruscalzo, A.; Londero, A. P.; Fröhlich, C.; Möllmann, U.; Schmitz, R.
2014-01-01
Aim. Feasibility and reliability of tissue Doppler imaging-(TDI-) based elastography for cervical quantitative stiffness assessment during all three trimesters of pregnancy were evaluated. Materials and Methods. Prospective case-control study including seventy-four patients collected between the 12th and 42nd weeks of gestation. The tissue strain (TS) was measured by two independent operators as natural strain. Intra- and interoperator intraclass correlation coefficient (ICC) agreements were evaluated. Results. TS measurement was always feasible and exhibited a high performance in terms of reliability (intraoperator ICC-agreement = 0.93; interoperator ICC agreement = 0.89 and 0.93 for a single measurement and for the average of two measurements, resp.). Cervical TS showed also a significant correlation with gestational age, cervical length, and parity. Conclusions. TS measurement during pregnancy demonstrated high feasibility and reliability. Furthermore, TS significantly correlated with gestational age, cervical length, and parity. PMID:24734246
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
Nanoscale Directional Motion towards Regions of Stiffness
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Liu, Min; Zhang, Guangqiao
2013-04-01
The present paper derivate the asymptotic solution of modal damping of one taut stay cable attached with one passive damper including damper stiffness and viscous damping. The effect of the damper stiffness on the modal damping of the stay cable-passive system was analytical investigated. On the basis of the asymptotic solution of modal damping of one stay cable attached with one passive damper with the effect of cable stiffness and by using the decay factor of damper stiffness and the decay factor of cable sag, maximum modal damping ratio and corresponding optimal damping coefficient, which indicates the relationships of the characteristics of the damper and the cable sag was theoretically analyzed. Numerical analysis of parameters on the effect of dynamic performance of the controlled stay cable was conducted.
The compressive stiffness of human pediatric heads.
Loyd, Andre Matthew; Nightingale, Roger W; Luck, Jason F; Song, Yin; Fronheiser, Lucy; Cutcliffe, Hattie; Myers, Barry S; Dale Bass, Cameron R
2015-11-01
Head injury is a persistent and costly problem for both children and adults. Globally, approximately 10 million people are hospitalized each year for head injuries. Knowing the structural properties of the head is important for modeling the response of the head in impact, and for providing insights into mechanisms of head injury. Hence, the goal of this study was to measure the sub-injurious structural stiffness of whole pediatric heads. 12 cadaveric pediatric (20-week-gestation to 16 years old) heads were tested in a battery of viscoelastic compression tests. The heads were compressed in both the lateral and anterior-posterior directions to 5% of gauge length at normalized deformation rates of 0.0005/s, 0.01/s, 0.1/s, and 0.3/s. Because of the non-linear nature of the response, linear regression models were used to calculate toe region (<2.5%) and elastic region (>2.5%) stiffness separately so that meaningful comparisons could be made across rate, age, and direction. The results showed that age was the dominant factor in predicting the structural stiffness of the human head. A large and statistically significant increase in the stiffness of both the toe region and the elastic region was observed with increasing age (p<0.0001), but no significant difference was seen across direction or normalized deformation rate. The stiffness of the elastic region increased from as low as 5 N/mm in the neonate to >4500 N/mm in the 16 year old. The changes in stiffness with age may be attributed to the disappearance of soft sutures and the thickening of skull bones with age. PMID:26476760
Arterial stiffness, pulse pressure, and the kidney.
Safar, Michel E; Plante, Gérard E; Mimran, Albert
2015-05-01
Classical studies indicate that the contribution of kidneys to hypertension is almost exclusively related to the association between mean arterial pressure (MAP) and vascular resistance. Recent reports including estimates of glomerular filtration rate (GFR) have shown that pulse pressure (PP) and pulse wave velocity, 2 major indices of arterial stiffness, now emerge as significant predictors of cardiovascular risk and age-associated decline in GFR. Such findings are mainly observed in patients with hypertension and renal failure and in atherosclerotic subjects undergoing coronary angiography. In such patients, amplification of PP between ascending and terminal aorta at the renal site is constantly increased over 10mm Hg (P < 0.001), whereas MAP level remains continuously unmodified. This PP amplification is significantly associated with presence of proteinuria. Furthermore, increases in plasma creatinine and aortic stiffness are independently and positively correlated (P < 0.001) both in cross-sectional and longitudinal studies. All these relationships associating PP, arterial stiffness, and renal function are mainly observed in patients 60 years of age or older. Furthermore, in renal transplant patients and their donors, subjects have been recruited for evaluations of arterial stiffness and posttransplant decline in GFR. Determinants of GFR decline were evaluated 1 and 9 years after transplantation. The first year GFR decline was related to smoking and acute rejection, whereas the later was significantly and exclusively associated with donor age and aortic stiffness. Thus, in hypertensive humans, the observed association between PP and GFR suggests that the 2 parameters are substantially mediated by arterial stiffness, not exclusively by vascular resistance. PMID:25480804
Wang, Joong-San; Um, Gi-Mai; Choi, Jung-Hyun
2016-01-01
[Purpose] This study aimed to examine the immediate effects of kinematic taping on the tone and stiffness in the leg muscles of subjects with flexible flat feet. [Subjects and Methods] A total of 30 subjects, 15 in the kinematic taping and 15 in the sham taping group, were administered respective taping interventions. Subsequently, the foot pressure and the tone and stiffness in the tibialis anterior, rectus femoris, medial gastrocnemius, and the long head of the biceps femoris muscles of both the lower extremities were measured. [Results] The foot pressure of the dominant leg significantly decreased in the kinematic taping group. The muscle tone and stiffness in the rectus femoris muscle of the dominant and non-dominant leg, tibialis anterior muscle of the dominant leg, medial gastrocnemius muscle of the non-dominant leg, and the stiffness in the dominant leg significantly decreased. The muscle tone and stiffness generally increased in the sham taping group. However, no significant difference was observed between the 2 groups. [Conclusion] This study demonstrated that kinematic taping on flexible flat feet had positive effects of immediately reducing the abnormally increased foot pressure and the tone and stiffness in the lower extremity muscles. PMID:27190479
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.
Baker, Erin L; Lu, Jing; Yu, Dihua; Bonnecaze, Roger T; Zaman, Muhammad H
2010-10-01
While significant advances have been made toward revealing the molecular mechanisms that influence breast cancer progression, much less is known about the associated cellular mechanical properties. To this end, we use particle-tracking microrheology to investigate the interplay among intracellular mechanics, three-dimensional matrix stiffness, and transforming potential in a mammary epithelial cell (MEC) cancer progression series. We use a well-characterized model system where human-derived MCF10A MECs overexpress either ErbB2, 14-3-3ζ, or both ErbB2 and 14-3-3ζ, with empty vector as a control. Our results show that MECs possessing ErbB2 transforming potential stiffen in response to elevated matrix stiffness, whereas non-transformed MECs or those overexpressing only 14-3-3ζ do no exhibit this response. We further observe that overexpression of ErbB2 alone is associated with the highest degree of intracellular sensitivity to matrix stiffness, and that the effect of transforming potential on intracellular stiffness is matrix-stiffness-dependent. Moreover, our intracellular stiffness measurements parallel cell migration behavior that has been previously reported for these MEC sublines. Given the current knowledge base of breast cancer mechanobiology, these findings suggest that there may be a positive relationship among intracellular stiffness sensitivity, cell motility, and perturbed mechanotransduction in breast cancer. PMID:20923638
Apparatus for measurement of coefficient of friction
NASA Technical Reports Server (NTRS)
Slifka, A. J.; Siegwarth, J. D.; Sparks, L. L.; Chaudhuri, Dilip K.
1990-01-01
An apparatus designed to measure the coefficient of friction in certain controlled atmospheres is described. The coefficient of friction observed during high-load tests was nearly constant, with an average value of 0.56. This value is in general agreement with that found in the literature and also with the initial friction coefficient value of 0.67 measured during self-mated friction of 440C steel in an oxygen environment.
NASA Technical Reports Server (NTRS)
Majda, George
1986-01-01
One-leg and multistep discretizations of variable-coefficient linear systems of ODEs having both slow and fast time scales are investigated analytically. The stability properties of these discretizations are obtained independent of ODE stiffness and compared. The results of numerical computations are presented in tables, and it is shown that for large step sizes the stability of one-leg methods is better than that of the corresponding linear multistep methods.
Computer program performs stiffness matrix structural analysis
NASA Technical Reports Server (NTRS)
Bamford, R.; Batchelder, R.; Schmele, L.; Wada, B. K.
1968-01-01
Computer program generates the stiffness matrix for a particular type of structure from geometrical data, and performs static and normal mode analyses. It requires the structure to be modeled as a stable framework of uniform, weightless members, and joints at which loads are applied and weights are lumped.
Vibrating Beam With Spatially Periodic Stiffness
NASA Technical Reports Server (NTRS)
Townsend, John S.
1989-01-01
Report presents theoretical analysis of vibrations of simply supported beam, bending stiffness varying about steady value, sinusoidally with position along length. Problem of practical importance because related to vibrations of twisted-pair electric-power transmission lines. Twists promote nonuniform shedding of vortexes and prevents resonant accumulation of vibrational energy from wind.
[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 μg 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
49 CFR 213.359 - Track stiffness.
Code of Federal Regulations, 2010 CFR
2010-10-01
..., DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness. (a) Track shall have a sufficient vertical strength to withstand the maximum vehicle loads generated at maximum permissible train speeds, cant deficiencies and surface defects. For...
49 CFR 213.359 - Track stiffness.
Code of Federal Regulations, 2012 CFR
2012-10-01
..., DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness. (a) Track shall have a sufficient vertical strength to withstand the maximum vehicle loads generated at maximum permissible train speeds, cant deficiencies and surface defects. For...
49 CFR 213.359 - Track stiffness.
Code of Federal Regulations, 2013 CFR
2013-10-01
..., DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness. (a) Track shall have a sufficient vertical strength to withstand the maximum vehicle loads generated at maximum permissible train speeds, cant deficiencies and surface defects. For...
49 CFR 213.359 - Track stiffness.
Code of Federal Regulations, 2014 CFR
2014-10-01
..., DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness. (a) Track shall have a sufficient vertical strength to withstand the maximum vehicle loads generated at maximum permissible train speeds, cant deficiencies and surface defects. For...
49 CFR 213.359 - Track stiffness.
Code of Federal Regulations, 2011 CFR
2011-10-01
..., DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Train Operations at Track Classes 6 and Higher § 213.359 Track stiffness. (a) Track shall have a sufficient vertical strength to withstand the maximum vehicle loads generated at maximum permissible train speeds, cant deficiencies and surface defects. For...
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…
On Burnett coefficients in periodic media
NASA Astrophysics Data System (ADS)
Conca, Carlos; Orive, Rafael; Vanninathan, Muthusamy
2006-03-01
The aim of this work is to demonstrate a curious property of general periodic structures. It is well known that the corresponding homogenized matrix is positive definite. We calculate here the next order Burnett coefficients associated with such structures. We prove that these coefficients form a tensor which is negative semidefinite. We also provide some examples showing degeneracy in multidimension.
NASA Astrophysics Data System (ADS)
Ishii, Yosuke; Biwa, Shiro
The transmission characteristics of ultrasonic wave impinging obliquely on composite laminates are analyzed. Incorporating the influence of thin resin-rich regions between adjacent plies by spring-type interfaces, the amplitude transmission coefficient of a unidirectional composite laminate immersed in water is calculated by the stiffness-matrix method. Using Floquet's theorem, the dispersion relation for the infinitely laminated structure is also calculated. Comparison between two results reveals that the frequency band-gaps in the dispersion relation agree well with the low-transmission frequency ranges of the finite laminated case. Comparing with the experimental transmission coefficients for an 11-ply carbon-epoxy composite laminate, the theoretical results are verified.
Shah, S N R; Sulong, N H Ramli; Shariati, Mahdi; Jumaat, M Z
2015-01-01
Steel pallet rack (SPR) beam-to-column connections (BCCs) are largely responsible to avoid the sway failure of frames in the down-aisle direction. The overall geometry of beam end connectors commercially used in SPR BCCs is different and does not allow a generalized analytic approach for all types of beam end connectors; however, identifying the effects of the configuration, profile and sizes of the connection components could be the suitable approach for the practical design engineers in order to predict the generalized behavior of any SPR BCC. This paper describes the experimental behavior of SPR BCCs tested using a double cantilever test set-up. Eight sets of specimens were identified based on the variation in column thickness, beam depth and number of tabs in the beam end connector in order to investigate the most influential factors affecting the connection performance. Four tests were repeatedly performed for each set to bring uniformity to the results taking the total number of tests to thirty-two. The moment-rotation (M-θ) behavior, load-strain relationship, major failure modes and the influence of selected parameters on connection performance were investigated. A comparative study to calculate the connection stiffness was carried out using the initial stiffness method, the slope to half-ultimate moment method and the equal area method. In order to find out the more appropriate method, the mean stiffness of all the tested connections and the variance in values of mean stiffness according to all three methods were calculated. The calculation of connection stiffness by means of the initial stiffness method is considered to overestimate the values when compared to the other two methods. The equal area method provided more consistent values of stiffness and lowest variance in the data set as compared to the other two methods. PMID:26452047
Shah, S. N. R.; Sulong, N. H. Ramli; Shariati, Mahdi; Jumaat, M. Z.
2015-01-01
Steel pallet rack (SPR) beam-to-column connections (BCCs) are largely responsible to avoid the sway failure of frames in the down-aisle direction. The overall geometry of beam end connectors commercially used in SPR BCCs is different and does not allow a generalized analytic approach for all types of beam end connectors; however, identifying the effects of the configuration, profile and sizes of the connection components could be the suitable approach for the practical design engineers in order to predict the generalized behavior of any SPR BCC. This paper describes the experimental behavior of SPR BCCs tested using a double cantilever test set-up. Eight sets of specimens were identified based on the variation in column thickness, beam depth and number of tabs in the beam end connector in order to investigate the most influential factors affecting the connection performance. Four tests were repeatedly performed for each set to bring uniformity to the results taking the total number of tests to thirty-two. The moment-rotation (M-θ) behavior, load-strain relationship, major failure modes and the influence of selected parameters on connection performance were investigated. A comparative study to calculate the connection stiffness was carried out using the initial stiffness method, the slope to half-ultimate moment method and the equal area method. In order to find out the more appropriate method, the mean stiffness of all the tested connections and the variance in values of mean stiffness according to all three methods were calculated. The calculation of connection stiffness by means of the initial stiffness method is considered to overestimate the values when compared to the other two methods. The equal area method provided more consistent values of stiffness and lowest variance in the data set as compared to the other two methods. PMID:26452047
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.
Lamb Wave Stiffness Characterization of Composites Undergoing Thermal-Mechanical Aging
NASA Technical Reports Server (NTRS)
Seale, Michael D.; Madaras, Eric I.
2004-01-01
The introduction of new, advanced composite materials into aviation systems requires a thorough understanding of the long term effects of combined thermal and mechanical loading upon those materials. Analytical methods investigating the effects of intense thermal heating combined with mechanical loading have been investigated. The damage mechanisms and fatigue lives were dependent on test parameters as well as stress levels. Castelli, et al. identified matrix dominated failure modes for out-of-phase cycling and fiber dominated damage modes for in-phase cycling. In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. To help evaluate the effect of aging, a suitably designed Lamb wave measurement system is being used to obtain bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system works by exciting an antisymmetric Lamb wave and calculating the velocity at each frequency from the known transducer separation and the measured time-of-flight. The same peak in the waveforms received at various distances is used to measure the time difference between the signals. The velocity measurements are accurate and repeatable to within 1% resulting in reconstructed stiffness values repeatable to within 4%. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. A mechanical scanner is used to move the sensors over the surface to map the time-of-flight, velocity, or stiffnesses of the entire specimen. Access to only one side of the material is required and no immersion or couplants are required because the sensors are dry coupled to the surface of the plate. In this study, the elastic stiffnesses D(sub 11), D(sub 22), A(sub 44), and A(sub 55) as well as time-of-flight measurements for composite samples that have undergone combined thermal and mechanical aging for
Assessment of impact factors on shear wave based liver stiffness measurement.
Ling, Wenwu; Lu, Qiang; Quan, Jierong; Ma, Lin; Luo, Yan
2013-02-01
Shear wave based ultrasound elastographies have been implemented as non-invasive methods for quantitative assessment of liver stiffness. Nonetheless, there are only a few studies that have investigated impact factors on liver stiffness measurement (LSM). Moreover, standard examination protocols for LSM are still lacking in clinical practice. Our study aimed to assess the impact factors on LSM to establish its standard examination protocols in clinical practice. We applied shear wave based elastography point quantification (ElastPQ) in 21 healthy individuals to determine the impact of liver location (segments I-VIII), breathing phase (end-inspiration and end-expiration), probe position (sub-costal and inter-costal position) and examiner on LSM. Additional studies in 175 healthy individuals were also performed to determine the influence of gender and age on liver stiffness. We found significant impact of liver location on LSM, while the liver segment V displayed the lowest coefficient of variation (CV 21%). The liver stiffness at the end-expiration was significantly higher than that at the end-inspiration (P=2.1E-05). The liver stiffness was 8% higher in men than in women (3.8 ± 0.7 kPa vs. 3.5 ± 0.4 kPa, P=0.0168). In contrast, the liver stiffness was comparable in the different probe positions, examiners and age groups (P>0.05). In conclusion, this study reveals significant impact from liver location, breathing phase and gender on LSM, while furthermore strengthening the necessity for the development of standard examination protocols on LSM. PMID:23116805
Veijalainen, A; Tompuri, T; Haapala, E A; Viitasalo, A; Lintu, N; Väistö, J; Laitinen, T; Lindi, V; Lakka, T A
2016-08-01
Associations of cardiorespiratory fitness (CRF), physical activity (PA), sedentary behavior, and body fat percentage (BF%) with arterial stiffness and dilation capacity were investigated in 160 prepubertal children (83 girls) 6-8 years of age. We assessed CRF (watts/lean mass) by maximal cycle ergometer exercise test, total PA, structured exercise, unstructured PA, commuting to and from school, recess PA and total and screen-based sedentary behavior by questionnaire, BF% using dual-energy X-ray absorptiometry, and arterial stiffness and dilation capacity using pulse contour analysis. Data were adjusted for sex and age. Poorer CRF (standardized regression coefficient β = -0.297, P < 0.001), lower unstructured PA (β = -0.162, P = 0.042), and higher BF% (β = 0.176, P = 0.044) were related to higher arterial stiffness. When CRF, unstructured PA, and BF% were in the same model, only CRF was associated with arterial stiffness (β = -0.246, P = 0.006). Poorer CRF was also related to lower arterial dilation capacity (β = 0.316, P < 0.001). Children with low CRF (< median) and high BF% (≥ median; P = 0.002), low CRF and low unstructured PA (< median; P = 0.006) or children with low unstructured PA and high BF% (P = 0.005) had higher arterial stiffness than children in the opposite halves of these variables. Poor CRF was independently associated with increased arterial stiffness and impaired arterial dilation capacity among children. PMID:26220100
NASA Astrophysics Data System (ADS)
Jiang, Yao; Li, Tie-Min; Wang, Li-Ping
2015-09-01
This paper investigates the stiffness modeling of compliant parallel mechanism (CPM) based on the matrix method. First, the general compliance matrix of a serial flexure chain is derived. The stiffness modeling of CPMs is next discussed in detail, considering the relative positions of the applied load and the selected displacement output point. The derived stiffness models have simple and explicit forms, and the input, output, and coupling stiffness matrices of the CPM can easily be obtained. The proposed analytical model is applied to the stiffness modeling and performance analysis of an XY parallel compliant stage with input and output decoupling characteristics. Then, the key geometrical parameters of the stage are optimized to obtain the minimum input decoupling degree. Finally, a prototype of the compliant stage is developed and its input axial stiffness, coupling characteristics, positioning resolution, and circular contouring performance are tested. The results demonstrate the excellent performance of the compliant stage and verify the effectiveness of the proposed theoretical model. The general stiffness models provided in this paper will be helpful for performance analysis, especially in determining coupling characteristics, and the structure optimization of the CPM.
A review on in situ stiffness adjustment methods in MEMS
NASA Astrophysics Data System (ADS)
de Laat, M. L. C.; Pérez Garza, H. H.; Herder, J. L.; Ghatkesar, M. K.
2016-06-01
In situ stiffness adjustment in microelectromechanical systems is used in a variety of applications such as radio-frequency mechanical filters, energy harvesters, atomic force microscopy, vibration detection sensors. In this review we provide designers with an overview of existing stiffness adjustment methods, their working principle, and possible adjustment range. The concepts are categorized according to their physical working principle. It is concluded that the electrostatic adjustment principle is the most applied method, and narrow to wide ranges in stiffness can be achieved. But in order to obtain a wide range in stiffness change, large, complex devices were designed. Mechanical stiffness adjustment is found to be a space-effective way of obtaining wide changes in stiffness, but these methods are often discrete and require large tuning voltages. Stiffness adjustment through stressing effects or change in Young’s modulus was used only for narrow ranges. The change in second moment of inertia was used for stiffness adjustment in the intermediate range.
Efficient Estimation of Time-Varying Intrinsic and Reflex Stiffness
Ludvig, Daniel; Perreault, Eric J.; Kearney, Robert E.
2013-01-01
Dynamic joint stiffness defines the dynamic relationship between the position of the joint and the torque acting about it; hence it is important in the control of movement and posture. Joint stiffness consists of two components: intrinsic stiffness and reflex stiffness. Measuring intrinsic and reflex torques directly is not possible, thus estimating intrinsic and reflex stiffness is challenging. A further complication is that both intrinsic and reflex stiffness vary with joint position and torque. Thus, the measurement of dynamic joint stiffness during movement requires a time-varying algorithm. Recently we described an algorithm to estimate time-varying intrinsic and reflex stiffness and demonstrated its application. This paper describes modifications to that algorithm that significantly improves the accuracy of the estimates it generates while increasing its computational efficiency by a factor of seven. PMID:22255247
Investigating bias in squared regression structure coefficients
Nimon, Kim F.; Zientek, Linda R.; Thompson, Bruce
2015-01-01
The importance of structure coefficients and analogs of regression weights for analysis within the general linear model (GLM) has been well-documented. The purpose of this study was to investigate bias in squared structure coefficients in the context of multiple regression and to determine if a formula that had been shown to correct for bias in squared Pearson correlation coefficients and coefficients of determination could be used to correct for bias in squared regression structure coefficients. Using data from a Monte Carlo simulation, this study found that squared regression structure coefficients corrected with Pratt's formula produced less biased estimates and might be more accurate and stable estimates of population squared regression structure coefficients than estimates with no such corrections. While our findings are in line with prior literature that identified multicollinearity as a predictor of bias in squared regression structure coefficients but not coefficients of determination, the findings from this study are unique in that the level of predictive power, number of predictors, and sample size were also observed to contribute bias in squared regression structure coefficients. PMID:26217273
Stiffness and mass matrices for shells of revolution (SAMMSOR II)
NASA Technical Reports Server (NTRS)
Tillerson, J. R.; Haisler, W. E.
1974-01-01
Utilizing element properties, structural stiffness and mass matrices are generated for as many as twenty harmonics and stored on magnetic tape. Matrices generated constitute input data to be used by other stiffness of revolution programs. Variety of boundary and loading conditions can be employed without having to create new mass and stiffness matrices for each case.
Direct measurement of the intrinsic ankle stiffness during standing.
Vlutters, M; Boonstra, T A; Schouten, A C; van der Kooij, H
2015-05-01
Ankle stiffness contributes to standing balance, counteracting the destabilizing effect of gravity. The ankle stiffness together with the compliance between the foot and the support surface make up the ankle-foot stiffness, which is relevant to quiet standing. The contribution of the intrinsic ankle-foot stiffness to balance, and the ankle-foot stiffness amplitude dependency remain a topic of debate in the literature. We therefore developed an experimental protocol to directly measure the bilateral intrinsic ankle-foot stiffness during standing balance, and determine its amplitude dependency. By applying fast (40 ms) ramp-and-hold support surface rotations (0.005-0.08 rad) during standing, reflexive contributions could be excluded, and the amplitude dependency of the intrinsic ankle-foot stiffness was investigated. Results showed that reflexive activity could not have biased the torque used for estimating the intrinsic stiffness. Furthermore, subjects required less recovery action to restore balance after bilateral rotations in opposite directions compared to rotations in the same direction. The intrinsic ankle-foot stiffness appears insufficient to ensure balance, ranging from 0.93±0.09 to 0.44±0.06 (normalized to critical stiffness 'mgh'). This implies that changes in muscle activation are required to maintain balance. The non-linear stiffness decrease with increasing rotation amplitude supports the previous published research. With the proposed method reflexive effects can be ruled out from the measured torque without any model assumptions, allowing direct estimation of intrinsic stiffness during standing. PMID:25843262
Rhee, Moo-Yong; Chang, Hyun Kyu; Kim, Seong-Kyu
2007-06-01
Behçet's disease (BD) is a systemic vasculitis involving diverse sizes of arteries and veins. We performed this study to evaluate the vascular changes by assessment of the arterial stiffness and intima-media thickness (IMT) of carotid artery in Korean patients with BD. Forty-one patients with BD and age-, and sex-matched 53 healthy subjects were recruited in this study. Carotid arterial stiffness and IMT were assessed by using high-resolution B-mode ultrasonography. Arterial stiffness parameters such as carotid arterial distensibility coefficient, stiffness index, and incremental elastic modulus (E(inc)) were significantly increased in BD patients compared with those in healthy subjects, but not in IMT. Positive relationship was noted between age and IMT, whereas age of onset was significantly associated with arterial stiffness in BD. This finding suggests impaired endothelial function before visible structural changes of arterial wall in BD. Age and age of onset may be an independent risk factor for carotid IMT and arterial stiffness, respectively. Further studies in more large populations are required to confirm our results. PMID:17596642
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
Electron profile stiffness and critical gradient studies
DeBoo, J. C.; Petty, C. C.; Burrell, K. H.; Smith, S. P.; White, A. E.; Doyle, E. J.; Hillesheim, J. C.; Rhodes, T. L.; Schmitz, L.; Wang, G.; Zeng, L.; Holland, C.; McKee, G. R.
2012-08-15
Electron profile stiffness was studied in DIII-D L-mode discharges by systematically varying the heat flux in a narrow region with electron cyclotron heating and measuring the local change produced in {nabla}T{sub e}. Electron stiffness was found to slowly increase with toroidal rotation velocity. A critical inverse temperature gradient scale length 1/L{sub C} {approx} 3 m{sup -1} was identified at {rho}=0.6 and found to be independent of rotation. Both the heat pulse diffusivity and the power balance diffusivity, the latter determined by integrating the measured dependence of the heat pulse diffusivity on -{nabla}T{sub e}, were fit reasonably well by a model containing a critical inverse temperature gradient scale length and varying linearly with 1/L{sub T} above the threshold.
Effect of chain stiffness on polymer properties
NASA Astrophysics Data System (ADS)
Luettmer-Strathmann, Jutta
2008-03-01
Static and dynamic properties of polymers are affected by the stiffness of the chains. In this work, we investigate structural and thermodynamic properties of a lattice model for semiflexible polymer chains. The model is an extension of Shaffer's bond- fluctuation model and includes attractive interactions between monomers and an adjustable bending penalty that determines the Kuhn segment length. For isolated chains, a competition between monomer-monomer interactions and bending penalties determines the chain conformations at low temperatures. For dense melts, packing effects play an important role in the structure and thermodynamics of the polymeric liquid. In order to investigate static properties as a function of temperature and chain stiffness, we perform Wang-Landau type simulations and construct densities of states over the two-dimensional state space of monomer-monomer and bending contributions to the internal energy.
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
Stiff modes in spinvalve simulations with OOMMF
NASA Astrophysics Data System (ADS)
Mitropoulos, Spyridon; Tsiantos, Vassilis; Ovaliadis, Kyriakos; Kechrakos, Dimitris; Donahue, Michael
2016-04-01
Micromagnetic simulations are an important tool for the investigation of magnetic materials. Micromagnetic software uses various techniques to solve differential equations, partial or ordinary, involved in the dynamic simulations. Euler, Runge-Kutta, Adams, and BDF (Backward Differentiation Formulae) are some of the methods used for this purpose. In this paper, spinvalve simulations are investigated. Evidence is presented showing that these systems have stiff modes, and that implicit methods such as BDF are more effective than explicit methods in such cases.
Strong and stiff aramid nanofiber/carbon nanotube nanocomposites.
Zhu, Jiaqi; Cao, Wenxin; Yue, Mingli; Hou, Ying; Han, Jiecai; Yang, Ming
2015-03-24
Small but strong carbon nanotubes (CNTs) are fillers of choice for composite reinforcement owing to their extraordinary modulus and strength. However, the mechanical properties of the nanocomposites are still much below those for mechanical parameters of individual nanotubes. The gap between the expectation and experimental results arises not only from imperfect dispersion and poor load transfer but also from the unavailability of strong polymers that can be effectively utilized within the composites of nanotubes. Aramid nanofibers (ANFs) with analogous morphological features to nanotubes represent a potential choice to complement nanotubes given their intrinsic high mechanical performance and the dispersible nature, which enables solvent-based processing methods. In this work, we showed that composite films made from ANFs and multiwalled CNTs (MWCNTs) by vacuum-assisted flocculation and vacuum-assisted layer-by-layer assembly exhibited high ultimate strength of up to 383 MPa and Young's modulus (stiffness) of up to 35 GPa, which represent the highest values among all the reported random CNT nanocomposites. Detailed studies using different imaging and spectroscopic characterizations suggested that the multiple interfacial interactions between nanotubes and ANFs including hydrogen bonding and π-π stacking are likely the key parameters responsible for the observed mechanical improvement. Importantly, our studies further revealed the attractive thermomechanical characteristics of these nanocomposites with high thermal stability (up to 520 °C) and ultralow coefficients of thermal expansion (2-6 ppm·K(-1)). Our results indicated that ANFs are promising nanoscale building blocks for functional ultrastrong and stiff materials potentially extendable to nanocomposites based on other nanoscale fillers. PMID:25712334
Davis, J.L.; Grant, J.W.
2014-01-01
Anatomically correct turtle utricle geometry was incorporated into two finite element models. The geometrically accurate model included appropriately shaped macular surface and otoconial layer, compact gel and column filament (or shear) layer thicknesses and thickness distributions. The first model included a shear layer where the effects of hair bundle stiffness was included as part of the shear layer modulus. This solid 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 Pascals. We feel this is the most accurate prediction of this shear layer modulus and fits with other estimates (Kondrachuk, 2001b). The second model incorporated only beam elements in the shear layer to represent hair cell bundle stiffness. The beam element 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
Defining Normal Liver Stiffness Range in a Normal Healthy Chinese Population without Liver Disease
Fung, James; Lee, Cheuk-kwong; Chan, Monica; Seto, Wai-kay; Wong, Danny Ka-ho; Lai, Ching-lung; Yuen, Man-fung
2013-01-01
Background For patients with chronic liver disease, different optimal liver stiffness cut-off values correspond to different stages of fibrosis, which are specific for the underlying liver disease and population. Aims To establish the normal ranges of liver stiffness in the healthy Chinese population without underlying liver disease. Methods This is a prospective cross sectional study of 2,528 healthy volunteers recruited from the general population and the Red Cross Transfusion Center in Hong Kong. All participants underwent a comprehensive questionnaire survey, measurement of weight, height, and blood pressure. Fasting liver function tests, glucose and cholesterol was performed. Abdominal ultrasound and transient elastography were performed on all participants. Results Of the 2,528 subjects, 1,998 were excluded with either abnormal liver parenchyma on ultrasound, chronic medical condition, abnormal blood tests including liver enzymes, fasting glucose, fasting cholesterol, high body mass index, high blood pressure, or invalid liver stiffness scan. The reference range for the 530 subjects without known liver disease was 2.3 to 5.9 kPa (mean 4.1, SD 0.89). The median liver stiffness was higher in males compared with females (4.3 vs 4.0 kPa respectively, p<0.001). There was also a decline in median Lliver stiffness in the older age group, from 4.2 kPa in those <25 years to 3.4 kPa for those >55 years (p=0.001). Conclusions The healthy reference range for liver stiffness in the Chinese population is 2.3 to 5.9 kPa. Female gender and older age group was associated with a lower median liver stiffness. PMID:24386446
Prediction of apparent trabecular bone stiffness through fourth-order fabric tensors.
Moreno, Rodrigo; Smedby, Örjan; Pahr, Dieter H
2016-08-01
The apparent stiffness tensor is an important mechanical parameter for characterizing trabecular bone. Previous studies have modeled this parameter as a function of mechanical properties of the tissue, bone density, and a second-order fabric tensor, which encodes both anisotropy and orientation of trabecular bone. Although these models yield strong correlations between observed and predicted stiffness tensors, there is still space for reducing accuracy errors. In this paper, we propose a model that uses fourth-order instead of second-order fabric tensors. First, the totally symmetric part of the stiffness tensor is assumed proportional to the fourth-order fabric tensor in the logarithmic scale. Second, the asymmetric part of the stiffness tensor is derived from relationships among components of the harmonic tensor decomposition of the stiffness tensor. The mean intercept length (MIL), generalized MIL (GMIL), and fourth-order global structure tensor were computed from images acquired through microcomputed tomography of 264 specimens of the femur. The predicted tensors were compared to the stiffness tensors computed by using the micro-finite element method ([Formula: see text]FE), which was considered as the gold standard, yielding strong correlations ([Formula: see text] above 0.962). The GMIL tensor yielded the best results among the tested fabric tensors. The Frobenius error, geodesic error, and the error of the norm were reduced by applying the proposed model by 3.75, 0.07, and 3.16 %, respectively, compared to the model by Zysset and Curnier (Mech Mater 21(4):243-250, 1995) with the second-order MIL tensor. From the results, fourth-order fabric tensors are a good alternative to the more expensive [Formula: see text]FE stiffness predictions. PMID:26341838
Coefficients of Effective Length.
ERIC Educational Resources Information Center
Edwards, Roger H.
1981-01-01
Under certain conditions, a validity Coefficient of Effective Length (CEL) can produce highly misleading results. A modified coefficent is suggested for use when empirical studies indicate that underlying assumptions have been violated. (Author/BW)
Exchange stiffness of Ca-doped YIG
NASA Astrophysics Data System (ADS)
Avgin, I.; Huber, D. L.
1994-05-01
An effective medium theory for the zero-temperature exchange stiffness of uncompensated Ca-doped YIG is presented. The theory is based on the assumption that the effect of the Ca impurities is to produce strong, random ferromagnetic interactions between spins on the a and d sublattices. In the simplest version of the theory, a fraction, x, of the ad exchange integrals are large and positive, x being related to the Ca concentration. The stiffness is calculated as function of x for arbitrary perturbed ad exchange integral, Jxad. For Jxad≳(1/5)‖8Jaa+3Jdd‖, with Jaa and Jdd denoting the aa and dd exchange integrals, respectively, there is a critical concentration, Xc, such that when x≳Xc, the stiffness is complex. It is suggested that Xc delineates the region where there are significant departures from colinearity in the ground state of the Fe spins. Extension of the theory to a model where the Ca doping is assumed to generate Fe4+ ions on the tetrahedral sites is discussed. Possible experimental tests of the theory are mentioned.
Age, arterial stiffness, and components of blood pressure in Chinese adults.
Zheng, Meili; Xu, Xiping; Wang, Xiaobin; Huo, Yong; Xu, Xin; Qin, Xianhui; Tang, Genfu; Xing, Houxun; Fan, Fangfang; Cui, Wei; Yang, Xinchun
2014-12-01
Blood pressure (BP) changes with age. We conducted a cross-sectional study in rural Chinese adults to investigate: (1) what is the relationship between age, arterial stiffness, and BP in Chinese men and women; and (2) to what degree can the age-BP relationship be explained by arterial stiffness, controlling for other covariables. These analyses included a total of 1688 subjects (males/females: 623/1065), aged 40 to 88 years. Among them, 353 (20.9%) had hypertension (defined as systolic blood pressure (SBP) ≥ 140 mm Hg or diastolic blood pressure (DBP) ≥ 90 mm Hg). Arterial stiffness was measured by brachial-ankle pulse wave velocity (baPWV). baPWV appeared to be more strongly correlated with BP (including SBP, DBP, mean arterial pressure [MAP], pulse pressure [PP]) than age (P < 0.001 for comparisons between Spearman correlation coefficients). Furthermore, baPWV was associated with BP (including SBP, DBP, MAP, and PP) and risk of hypertension in a dose-response fashion, independent of age; in contrast, the age-BP associations were either attenuated or became negative after adjusting for baPWV. Arterial stiffness appears to be an independent contributor to hypertension, even after adjusting for age and other covariables. In contrast, age-BP associations became attenuated or negative after adjusting for baPWV. The utility of baPWV as a diagnostic, prognostic, and therapeutic indicator for hypertension warrants further investigation. PMID:25546666
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
NASA Technical Reports Server (NTRS)
Kibler, K. S.; Mcdaniel, G. A.
1981-01-01
A digital local linearization technique was used to solve a system of stiff differential equations which simulate a magnetic bearing assembly. The results prove the technique to be accurate, stable, and efficient when compared to a general purpose variable order Adams method with a stiff option.
Identifying Bearing Rotordynamic Coefficients using an Extended Kalman Filter
NASA Technical Reports Server (NTRS)
Miller, Bard A.; Howard, Samuel A.
2008-01-01
An Extended Kalman Filter is developed to estimate the linearized direct and indirect stiffness and damping force coefficients for bearings in rotor-dynamic applications from noisy measurements of the shaft displacement in response to imbalance and impact excitation. The bearing properties are modeled as stochastic random variables using a Gauss-Markov model. Noise terms are introduced into the system model to account for all of the estimation error, including modeling errors and uncertainties and the propagation of measurement errors into the parameter estimates. The system model contains two user-defined parameters that can be tuned to improve the filter s performance; these parameters correspond to the covariance of the system and measurement noise variables. The filter is also strongly influenced by the initial values of the states and the error covariance matrix. The filter is demonstrated using numerically simulated data for a rotor-bearing system with two identical bearings, which reduces the number of unknown linear dynamic coefficients to eight. The filter estimates for the direct damping coefficients and all four stiffness coefficients correlated well with actual values, whereas the estimates for the cross-coupled damping coefficients were the least accurate.
Identifying Bearing Rotodynamic Coefficients Using an Extended Kalman Filter
NASA Technical Reports Server (NTRS)
Miller, Brad A.; Howard, Samuel A.
2008-01-01
An Extended Kalman Filter is developed to estimate the linearized direct and indirect stiffness and damping force coefficients for bearings in rotor dynamic applications from noisy measurements of the shaft displacement in response to imbalance and impact excitation. The bearing properties are modeled as stochastic random variables using a Gauss-Markov model. Noise terms are introduced into the system model to account for all of the estimation error, including modeling errors and uncertainties and the propagation of measurement errors into the parameter estimates. The system model contains two user-defined parameters that can be tuned to improve the filter's performance; these parameters correspond to the covariance of the system and measurement noise variables. The filter is also strongly influenced by the initial values of the states and the error covariance matrix. The filter is demonstrated using numerically simulated data for a rotor bearing system with two identical bearings, which reduces the number of unknown linear dynamic coefficients to eight. The filter estimates for the direct damping coefficients and all four stiffness coefficients correlated well with actual values, whereas the estimates for the cross-coupled damping coefficients were the least accurate.
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.
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)
Padovan, J.; Lackney, J.
1986-01-01
The current paper develops a constrained hierarchical least square nonlinear equation solver. The procedure can handle the response behavior of systems which possess indefinite tangent stiffness characteristics. Due to the generality of the scheme, this can be achieved at various hierarchical application levels. For instance, in the case of finite element simulations, various combinations of either degree of freedom, nodal, elemental, substructural, and global level iterations are possible. Overall, this enables a solution methodology which is highly stable and storage efficient. To demonstrate the capability of the constrained hierarchical least square methodology, benchmarking examples are presented which treat structure exhibiting highly nonlinear pre- and postbuckling behavior wherein several indefinite stiffness transitions occur.
Bending stiffness of conical and standard external fixator pins.
Oni, O O; Capper, M; Soutis, C
1993-10-01
The bending stiffnesses of a conical and a standard external fixator pin have been compared. The pins were inserted into pilot holes in a piece of teak hardwood and loads of different magnitudes were applied at a fixed moment arm. Force-deflection curves were obtained for each pin, and stiffness (newtons per metre) and percentage stiffness reduction were calculated for each pilot hole size. The results show that deflection increased (i.e. stiffness decreased) with increasing force or diameter of pilot hole. This loss of stiffness was linear for the standard pin but was bimodal for the conical pin. PMID:8286671