Showing papers on "Elasticity (economics) published in 1999"

Contact, Adhesion and Rupture of Elastic Solids

Abstract: 1 Elements of Surface Physics.- 2 Elements of Elasticity.- 3 Rupture and Adherence of Elastic Solids.- 4 Frictionless Elastic Contact.- 5 Study of Some Geometries.- Appendix A.- References.- Appendix B.

Strain gradient interpretation of size effects

Abstract: It is shown that the phenomenon of strength dependence on size, for otherwise geometrically similar specimens, may be interpreted on the basis of gradient elasticity and gradient plasticity arguments. This is illustrated by adopting a simple strength of materials approach for considering torsion and bending of solid bars and subsequent comparison with available experimental data. Solutions of boundary value problems based on gradient elasticity and gradient plasticity including those of fracture and shear banding can also be used to interpret size effects in more complex situations. This is not discussed here, however, in order to maintain simplicity and clarity when illustrating the theoretical predictions in comparison with the experimental trends.

Speckle tracking methods for ultrasonic elasticity imaging using short-time correlation

Abstract: In ultrasound elasticity imaging, strain decorrelation is a major source of error in displacements estimated using correlation techniques. This error can be significantly decreased by reducing the correlation kernel. Additional gains in signal-to-noise ratio (SNR) are possible by filtering the correlation functions prior to displacement estimation. Tradeoffs between spatial resolution and estimate variance are discussed, and estimation in elasticity imaging is compared to traditional time-delay estimation. Simulations and experiments on gel-based phantoms are presented. The results demonstrate that high resolution, high SNR strain estimates can be computed using small correlation kernels (on the order of the autocorrelation width of the ultrasound signal) and correlation filtering.

Fluid Films with Curvature Elasticity

Abstract: The phenomenology of surfactant fluid-film microstructures interspersed in bulk fluids poses significant challenges to continuum theory. By using simple models of elastic surfaces, chemical physicists have been partially successful in describing the qualitative features of ...

Ultrasound velocity of trabecular cubes reflects mainly bone density and elasticity.

Abstract: Studies have indicated that quantitative ultrasound (QUS) variables may be influenced by the mechanical properties of bone which in turn are determined by bone's material and structural properties. However, from these studies it is unclear what role density, elasticity, and structure play in determining velocity. Eighteen defatted, 12-mm cubic trabecular bone specimens were cut from cadaveric specimens. Amplitude-dependent speed of sound (SOS) using a single point QUS system was assessed in three orthogonal axes. Magnetic resonance images were obtained, from which measures of apparent trabeuclar structure were derived. The specimens were nondestructively tested in compression along three orthogonal axes defined by the sides of the cubes. The elastic modulus (in the three directions) and the strength (in one direction) were determined. Trabecular BMD was measured by quantitative computed tomography. SOS varied significantly with direction of measurement, with the highest value in the axial direction (axial:1715 m/s, sagittal: 1662 m/second, and coronal: 1676 m/s). SOS of each of the three axes was generally associated with the various mechanical (r = 0.30–0.87), density (r = 0.81–0.93), and bone structural variables (0.3–0.8). However, after adjusting the SOS correlations by density, only the correlation with elasticity remained significant in the coronal direction. BMD alone explained 88–93% of variance in SOS whereas in the multivariate model, BMD plus elasticity and/or anisotropic variables explained 96–98% of the variance in SOS. Variability of SOS is explained mostly by density and to a small extent by elasticity or anisotropy. Since only 2–6% of the variance of the QUS measurement is not explained by density and elasticity, one could conclude that the remaining variance reflects other properties of bone or perhaps simply measurement error. Evidence that these other properties may be structure related is only found in the anisotropy of QUS parameter.

Elastic nonwoven fabric prepared from bi-component filaments

Abstract: A bonded web (W) of multi-component strands (F) that include a first polymeric component (1) and a second polymeric component (2) is capable of overcoming a number of problems associated with nonwoven webs including both stickiness and blocking. The first polymeric component (1) and second polymeric component (2) are arranged in substantially distinct zones extending longitudinally along at least a portion of a length of the strands (F) which make up the web (W) with the second component containing a zone constituting at least a portion of the peripheral surface of the strand. Moreover, the first polymeric component (1) has an elasticity which is greater than that of the second polymer component (2). A process producing elastomeric spunbonded nonwoven fabrics which utilizes air in attenuating and/or drawing of strands is also provided.

Hysteresis and the Dynamic Elasticity of Consolidated Granular Materials

Abstract: Quasistatic elasticity measurements on rocks show them to be strikingly nonlinear and to have elastic hysteresis with end point memory. When the model for this quasistatic elasticity is extended to the description of nonlinear dynamic elasticity the elastic elements responsible for the hysteresis dominate the behavior. Consequently, in a resonant bar, driven to nonlinearity, the frequency shift and the attenuation are predicted to be nonanalytic functions of the strain field. A resonant bar experiment yielding results in substantial qualitative and quantitative accord with these predictions is reported. {copyright} {ital 1999} {ital The American Physical Society }

On the topological derivative in shape optimization

Abstract: In this paper the topological derivative for an arbitrary shape functional is defined. Examples are provided for elliptic equations and the elasticity system in the plane. The topological derivative can be used for solving shape optimization problems in structural mechanics.

Segmented conformable breathable films

Abstract: Unitary films are provided having at least first and second film segments which extend adjacent one another and are permanently joined together. The first and second segments have different compositions whereby the unitary film includes distinct segments having varied physical properties such as, for example, varied levels of high water-vapor transmission rates and/or elasticity. The unitary films and laminates thereof are well suited for use as outer covers in personal care articles and various other barrier articles.

Finite Sample Thickness Effects on Elasticity Determination Using Atomic Force Microscopy

Abstract: Finite sample thickness effects on material elasticity measurements made using an atomic force microscope have been calculated. The model includes an elastic layer on an elastic foundation and simulates sample indentation under an applied load. Rigid axisymmetric tips with conical, paraboloidal, and hyperboloidal profiles are considered. The results show that a common approach to estimating elastic moduli from force−displacement curves can lead to a significant error that depends on the units of measurement. A method to unambiguously estimate and correct this error is proposed. In addition, it is shown that elasticity estimates for monolayer thick samples using the force−modulation technique can contain a substantial, sample thickness-dependent error. Local thickness variations can result in misleading contrast in force−modulation images for samples that are several nanometers thick.

Elasticity of an electron liquid

Abstract: The zero temperature response of an interacting electron liquid to a time-dependent vector potential of wave vector q and frequency w such that q > 1), where mu \sim nE_F and eta \sim 0.

The mixed mode crack problem in an inhomogeneous orthotropic medium

Abstract: The mixed mode crack problem in plane elasticity for a graded and oriented material is considered. The material property grading is intentional, whereas the property orientation or orthotropy is usually the consequence of material processing. It is assumed that the crack is located in a plane perpendicular to the direction of property grading and the principal axes of orthotropy are parallel and perpendicular to the crack. The four independent engineering constants E11, E22, G12, and ν12 are replaced by a stiffness parameter, E = √E11 E22, a stiffness ratio, δ = (E11/E22)1/4, a Poisson's ratio, ν = √ν12 ν21, and a shear parameter κ0 = (E/2G12) - ν. The corresponding mixed boundary value problem is reduced to a system of integral equations which is solved for various loading conditions and material parameters. The results presented consist of the strain energy release rate, the stress intensity factors and the crack opening displacements. It is found that generally the stress intensity factors increase with increasing material inhomogeneity parameter and shear parameter and with decreasing stiffness ratio.

Micropolar theory for two–dimensional stresses in elastic honeycomb

Abstract: A micropolar theory has been used to calculate the stress field generated by a fundamental boundaryvalue problem in planar elasticity; namely, a normal line force acting on the surface of a honeyco...

The concern of elasticity in stress-induced martensitic transformation in NiTi

Abstract: It has been reported in the literature that moduli of elasticity of the austenite and martensite of near-equiatomic NiTi differ often by a factor of 3. It is expected that a phase transformation between the two phases may be induced by the application of a stress, according to thermodynamic principles. This is due to the fact that the difference in elastic energy caused by the change in modulus of elasticity serves as a driving force for the transformation, similar to the effect of the lattice distortion of the martensite on the transformation. A thermodynamic equation expressing this effect is derived. It is expected, based on the understanding of this equation, that the relationship between the critical stress and the temperature for a thermoelastic martensitic transformation is non-linear if the transformation involves a large change in modulus of elasticity. Therefore, this equation may be used for either of two purposes: to clarify the reliability of the experimentally determined moduli of elasticity of the two phases or to verify the Clausius–Clapeyron relation between the critical stress and the temperature for the transformation.

Elasticity measurements show the existence of thin rigid cores inside mitotic chromosomes.

Abstract: Chromosome condensation is one of the most critical steps during cell division. However, the structure of condensed mitotic chromosomes is poorly understood. In this paper we describe a new approach based on elasticity measurements for studying the structure of in vitro assembled mitotic chromosomes in Xenopus egg extract. The approach is based on a unique combination of measurements of both longitudinal deformability and bending rigidity of whole chromosomes. By using specially designed micropipettes, the chromosome force–extension curve was determined. Analysis of the curvature fluctuation spectrum allowed for the measurement of chromosome bending ridigity. The relationship between the values of these two parameters is very specific: the measured chromosome flexibility was found to be 2,000 times lower than the flexibility calculated from the experimentally determined Young modulus. This requires the chromosome structure to be formed of one or a few thin rigid elastic axes surrounded by a soft envelope. The properties of these axes are well-described by models developed for the elasticity of titin-like molecules. Additionally, the deformability of in vitro assembled chromosomes was found to be very similar to that of native somatic chromosomes, thus demonstrating the existence of an essentially identical structure.

The effect of surfactant on the stability of a fluid filament embedded in a viscous fluid

Abstract: The effect of surfactant on the breakup of a viscous filament, initially at rest, surrounded by another viscous fluid is studied using linear stability analysis. The role of the surfactant is characterized by the elasticity number – a high elasticity number implies that surfactant is important. As expected, the surfactant slows the growth rate of disturbances. The influence of surfactant on the dominant wavenumber is less trivial. In the Stokes regime, the dominant wavenumber for most viscosity ratios increases with the elasticity number; for filament to matrix viscosity ratios ranging from about 0.03 to 0.4, the dominant wavenumber decreases when the elasticity number increases. Interestingly, a surfactant does not affect the stability of a filament when the surface tension (or Reynolds) number is very large.

Foamed resin compositions for sealing subterranean zones

Abstract: The present invention provides improved foamed hardenable epoxy resin sealing compositions and methods which are particularly useful in the construction and repair of wells. The foamed epoxy resin compositions are corrosion resistant and have improved mechanical properties including elasticity and ductility.

Electromechanics of ionoelastic beams as electrically controllable artificial muscles

Abstract: Presented are theoretical and experimental results on electrically controlled static and dynamic flexing and deformation of iono-elastic beams made with ionic-polymer metal composite (IPMC) artificial muscles. These composite materials have the capability of large motion sensing and actuation in a biomimetic fashion. The essence of the underlying iono-elastic response of such materials is due to Coulombic electro-dynamic charge interaction amongst a dispersed phase of metallic particles that are charged either positively or negatively, mobile phase of a cation such as hydrogen ions H+ (Protons) or Li+, Hydroxyl anions OH-, and a fixed anionic phase such as an assembly of sulfonates SO3- elastically attached to the backbone polymer network macromolecules. The mathematical model presented is analogous to classical Euler-Bernoulli's beam theory modified to accommodate a non-homoeneous distributed electrically-induced moment due to the presence of a non-homogeneous electric field in an elastic material. The presentation may be extended to materials governed by hyper- elasticity such as in rubber elasticity. Analytical solution obtained agree reasonably well with our experimental results on Cationic Polymer-Platinum Composites (CPPC) which are also reported in this paper.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Elasticity of MgSiO3 orthoenstatite

Abstract: The single-crystal elastic moduli of the MgSiO 3 orthoenstatite end-member have been measured by Brillouin spectroscopy at ambient conditions. The aggregate elastic moduli at 1 atm are KS = 107.6(15) GPa and μ = 76.8(7) GPa, for the adiabatic bulk modulus and shear modulus, respectively. These values are in excellent agreement with the results of previous acoustic studies of synthetic MgSiO3. Comparison of our results with pressure-volume ( P-V) measurements do not support the presence of a change in the P-V trajectory of orthoenstatite at ~4 GPa, as suggested previously on the basis of X-ray measurements to 8.5 GPa. The effects of chemical composition on the elasticity of orthopyroxenes are well represented by the variation of compressional and shear velocities with density, which exhibit well defined trends for both synthetic and natural samples.

Evaluation of mechanical materials properties by means of surface micromachined structures

Abstract: For all micromechanical devices, mechanical properties such as elasticity constants, internal stresses, fracture limits and, for ductile materials, yield limits and strain-hardening behaviour, are ...

When are Options Overpriced? The Black-Scholes Model and Alternative Characterisations of the Pricing Kernel

Abstract: An important determinant of option prices is the elasticity of the pricing kernel used to price all claims in the economy. In this paper, we first show that for a given forward price of the underlying asset, option prices are higher when the elasticity of the pricing kernel is declining than when it is constant. We then investigate the implications of the elasticity of the pricing kernel for the stochastic process followed by the underlying asset. Given that the underlying information process follows a geometric Brownian motion, we demonstrate that constant elasticity of the pricing kernel is equivalent to a Brownian motion for the forward price of the underlying asset, so that the Black-Scholes formula correctly prices options on the asset. In contrast, declining elasticity implies that the forward price process is no longer a Brownian motion: it has higher volatility and exhibits autocorrelation. In this case, the Black-Scholes formula underprices all options.

Structure and rheology of the defect-gel states of pure and particle-dispersed lyotropic lamellar phases

Abstract: We present important new results from light-microscopy and rheometry on a moderately concentrated lyotropic smectic, with and without particulate additives. Shear-treatment aligns the phase rapidly, except for a striking network of oily-streak defects, which anneals out much more slowly. If spherical particles several microns in diameter are dispersed in the lamellar medium, part of the defect network persists under shear-treatment, its nodes anchored on the particles. The sample as prepared has substantial storage and loss moduli, both of which decrease steadily under shear-treatment. Adding particles enhances the moduli and retards their decay under shear. The data for the frequency-dependent storage modulus after various durations of shear-treatment can be scaled to collapse onto a single curve. The elasticity and dissipation in these samples thus arises mainly from the defect network, not directly from the smectic elasticity and hydrodynamics.

Variable modulus corneal implant and fabrication methods

Abstract: An intracorneal implant has a geometry bounded by a ring-shaped section of a cone, approximating a section of a sphere. The intracorneal implant has at least one region of modified elasticity. Typically, the intracorneal implant will have two or more regions of modified elasticity circumferentially spaced around the implant. The regions of modified elasticity affect the cone angle of the implant within each region and hence the corrective power of each region on the cornea. The intracorneal ring implant can be used for correction of various refractive defects of the vision, in particular, astigmatism or astigmatism combined with myopia or hyperopia. The implant may be formed as a ring, split ring, gapped ring or one or more segments of a ring.

Elasticity Solution for a Radially Nonhomogeneous Hollow Circular Cylinder

Abstract: An exact elasticity solution is developed for a radially nonhomogeneous hollow circular cylinder of exponential Young's modulus and constant Poisson ' s ratio. In the solution, the cylinder is first approximated by a piecewise homogeneous one, of the same overall dimension and composed of perfectly bonded constituent homogeneous hollow circular cylinders. For each of the constituent cylinders, the solution can be obtained from the theory of homogeneous elasticity in terms of several constants'. In the limit case when the number of the constituent cylinders becomes unboundedly large and their thickness tends to infinitesimally small, the piecewise homogeneous hollow circular cylinder reverts to the original nonhomogeneous one, and the constants contained in the solutions for the constituent cylinders turn into continuous functions. These functions, governed by some systems of first-order ordinary differential equations with variable coefficients, stand for the exact elasticity solution of the nonhomogeneous cylinder. Rigorous and explicit solutions are worked out for the ordinary differential equation systems, and used to generate a number of numerical results. It is indicated in the discussion that the developed method can also be applied to hollow circular cylinders with arbitrary, continuous radial nonhomogeneity. Introduction The elasticity problem of a homogeneous hollow circular cyl- inder has sufficiently been treated in Muskhelishvili (1963), Timoshenko and Goodier (1970), Barber (1992), and in other monographs. This article investigates the same problem on the whole, except that the hollow cylinder concerned is of a radially nonhomogeneous material. Nonhomogeneous materials can frequently be found in nature as well as in man-made structures. Porous substances, laminated composites, dissimilar media, and many others can be categorized as nonhomogeneous materials. However, typically nonhomoge- neous materials seem to be those with elastic constants varying continuously in different spatial directions. Continuous nonhomogeneity is a direct generalization of homo- geneity in theory; besides, material nonhomogeneity becomes es- sential and must sufficiently be considered in a number of practical situations. For example, in seismic problems, the spatial variation of material constants cannot be neglected owing to the massive structure of the earth. It appears that previous references on the elastic nonhomoge- neity have been concentrated in the area of mixed boundary value, including crack problems. In earlier years, contact and similar problems were treated with use of integral transforms (Belik and Protsenko, 1967; Popov, 1973; Kassir and Chuaprasert, 1974; Bakirtas, 1980). Recently, using mainly the method of singular integral equation, there has been an intensive interest in crack problems (Delale and Erdogan, 1983; Erdogan, Kaya and Joseph, 1991a, 1991b; Gao and Kuang, 1992; Craster and Atkinson 1994; Choi, 1996). By successively extending the solution to a Fredholm integral equation of the first kind, Yong and Hanson (1994) solved some crack and contact problems for a nonhomogeneous medium.