Showing papers on "Elasticity (economics) published in 1980"

More on infinite elements

Abstract: The method of infinite elements is briefly reviewed. New more logical and general formulations of infinite elements are presented. The simplicity of the programming is emphasized. Results are given for elasticity and potential problems. Future extensions are discussed.

Material properties of femoral cancellous bone in axial loading. Part I: Time independent properties.

Abstract: The time independent material behavior of cylindrical specimens obtained from the cancelous bone of 20 cadaveric human femora were determined. In this part of the publication, the nominal values for compressive strength, limits of elasticity (yield point), strain, elastic modulus and apparent density are being reported for the cancellous bone of the femoral head and condyle. The correlations between the various parameters are analysed. A positive linear correlation between the four parameters compressive stength, limit of elasticity, modulus of elasticity and apparent density could not be excluded. The material properties vary considerably both within one single bone and between individuals. Compressive strength, modulus of elasticity and apparent density found for cancellous bone of the femoral head are greater than those found in the condyles. Within the condyles, compressive strength, elastic modulus and apparent density increase from the proximal parts to the parts closer to the joint. The medial femoral condyle showed higher compressive strength than the lateral one. Relating each of the three other parameters to the apparent density of the individual specimen did not result in equalizing the data for the material properties. This indicates that the mechanical properties of cancellous bone are strongly related to the direction of loading.

Material Properties of Femoral Cancellous Bone in Axial Loading

Abstract: The time independent material behavior of cylindrical specimens obtained from the cancellous bone of 20 cadaveric human femora were determined. In this part of the publication, the nominal values for compressive strength, limits of elasticity (yield point), strain, elastic modulus and apparent density are being reported for the cancellous bone of the femoral head and condyle. The correlations between the various parameters are analysed. A positive linear correlation between the four parameters compressive stength, limit of elasticity, modulus of elasticity and apparent density could not be excluded. The material properties vary considerably both within one single bone and between individuals. Compressive strength, modulus of elasticity and apparent density found for cancellous bone of the femoral head are greater than those found in the condyles. Within the condyles, compressive strength, elastic modulus and apparent density increase from the proximal parts to the parts closer to the joint. The medial femoral condyle showed higher compressive strength than the lateral one. Relating each of the three other parameters to the apparent density of the individual specimen did not result in equalizing the data for the material properties. This indicates that the mechanical properties of cancellous bone are strongly related to the direction of loading.

A reevaluation of price elasticities for irrigation water

Abstract: The effectiveness of pricing systems in the allocation of irrigation water is linked with the price elasticity of demand of farmers for water. Using microeconomic theory, it is shown that omission of the elasticity of demand for the crop produced leads to an inelastic bias in the demand for irrigated water. Linear programing approaches omit the product elasticity of demand and are consequently biased, whereas quadratic programing approaches to estimating derived demands for irrigation water include product demand functions. The difference between the resulting estimates are empirically demonstrated for regional derived demand functions estimated from a model of California's agricultural industry.

Elastic behaviour of YAG under pressure

Abstract: Measurements of the effects of hydrostatic and uniaxial pressures on ultrasonic wave velocities are used to obtain the six third-order elastic constants of yttrium aluminium garnet (YAG). Results are used to investigate whether the shear isotropy and the conformity with the Cauchy relation (indicative of central forces), which hold for the second-order elastic constants of YAG, extend into the region of finite strain which determines higher-order elasticity. The compression has been extrapolated up to 150*108 Pa using the Murnaghan equation of state. The vibrational anharmonicity of YAG and yttrium iron garnet (YIG) are compared through the acoustic-mode Gruneisen gammas computed from the pressure dependences of the elastic constants. The attenuation of transverse microwave ultrasonic waves propagated along the (001) direction (the mode used in acoustic devices) due to anharmonic interactions with thermal phonons, calculated at the limits omega tau >>1 and omega tau <1, is shown to be in good agreement with previous experimental attenuation measurements for this mode.

Vertical Vibration Analysis of Suspension Bridges

Abstract: A method of analysis is outlined for free vertical vibrations of suspension bridges. The method employs a digital computer and a finite element approach, and uses a linearized theory which restricts the amplitudes of vibrations to be small. The analysis is designed to determine the natural frequencies, modes of vibration, and energy storage capacities of the different members of the bridge. Both symmetric and antisymmetric modes of vibrations are considered. For the symmetric modes (which include additional vibrational cable tension), it is shown that it is imperative to include the elasticity of the cables if correct solutions are to be obtained. A detailed numerical example, which includes the effect of the extensibility of the cables and the elasticity of the towers, is presented and the results are examined by a comparison between measured and computed natural frequencies and mode shapes of a real bridge; the comparison shows good agreement.

Brain elasticity changes with ventriculomegaly

Abstract: ✓ The pressure-volume relationship of brain elasticity was determined in 32 patients during servo-controlled variable-rate lumbar infusions to measure net cerebrospinal fluid (CSF) absorptive capacity. Several indices were used to estimate ventricular size from computerized tomography scans. The results show a linear relationship between ventricular size and the elasticity slope which relates the natural logarithm of pressure to volume. It follows that a hydrocephalic patient should show a greater intracranial pulse amplitude at a given pressure than does a patient with normal-sized ventricles. Although these elasticity changes may simply be the result of the ventriculomegaly, it seems possible that the pressure-volume elasticity relationship may be of etiological importance in disorders of the CSF system.

Correcting for truncation bias in the analysis of experiments in time-of-day prcing of electricity

Abstract: This paper applies methods for analyzing data from samples that have been chosen by restricting the target population in discernable ways to data from a 1976 experiment in time-of-day pricing of electricity for residential customers in Arizona. We find that whereas conventional estimation methods lead to the conclusion that the peak price elasticity of demand is larger (in absolute value) than either the corresponding midpeak or offpeak elasticity, once truncation bias is accounted for, the peak elasticity is smaller than the other two. This finding accords with a preliminary analysis of data from Wisconsin, where no such sample truncation was present.

Elasticity and stability of a dense gel

Abstract: An extension of the normal Gibbs formulation of statistical mechanics is applied to gels with permenent cross-links. The formalism permits an evaluation of the free energy in the case where the gel is dense, taking full account of excluded volume. This theory yields the changes in osmotic pressure upon cross-linkage and allows fully for syneresis; it enables the full elasticity of the network to be calculated, including the bulk modulus. Corrections to the simple addition of the free energy terms from network and solution theories are obtained, and for the case of a network in equilibrium with pure solvent a particularly simple formula is found.

The mixed finite element method in plane elasticity

Abstract: Studies of the convergence and performance of the mixed finite element method in plane elasticity are reported. A completeness criterion is proposed, and convergence rates for stresses and strain energy, as predicted elsewhere, are quoted. An eigenvalue analysis of the mixed element matrix is carried out for various combinations of interpolations for displacements and stresses in a triangular and a rectangular element, and the results are discussed in relation to the completeness criterion. Finally, a triangular element with linear interpolations for stresses and displacements is formulated and its use is demonstrated on several numerical examples.

Theory of Vertical Control with Variable Proportions

Abstract: The effect of vertical integration by an input monopolist on the price of the final product and the derived demands are examined when the production is of CES and the demand for the final product is of constant elasticity. The results are proved by analytical methods. Specifically, when the elasticity of substitution is less than one, the price of the final product can decrease but, regardless of any conditions, the derived demand for the nonmonopolized input decreases. However, that of monopolized input decreases if and only if the elasticity of substitution exceeds the elasticity of demand.

Physiological features of the pressure-volume function of brain elasticity in man

Abstract: ✓ The intracranial pressure-volume relationship of brain elasticity was examined in 20 patients with suspected disorders of the cerebrospinal fluid (CSF) system. Elasticity measurements were made as the patients were studied with a servo-controlled lumbar infusion technique to measure CSF absorptive capacity. The data were evaluated to determine the relationship between intracranial pressure (ICP) and volume, and between ICP variability and the level of ICP. The results confirm the exponential nature of the pressure-volume elasticity function in patients who are not critically ill. Eight of the 20 patients were shown to have normal CSF absorptive capacities, and there was no difference between their elasticity measurements and those of patients with absorptive defects. In addition, ICP variability was shown to be linearly related to the actual level of ICP. The physiological features of the pressure-volume elasticity function are reviewed. Based on these considerations, the clinical value and significance...

On uniqueness in finite elasticity with general loading

Abstract: In many problems of interest the (Cauchy) surface traction is given as a function of position on the deformed surface. A class of loadings sufficiently general to include these problems is considered and within the context of finite elasticity a number of uniqueness results are established. A key ingredient is the result of Gurtin and Spector that uniqueness holds in any convex, stable set of deformations.

On Pseudo-elasticity of Living Tissues

Abstract: Publisher Summary This chapter discusses the pseudo-elasticity of living tissues; soft tissues, such as arteries, muscles, skin, lung, and ureter have been considered. The mechanical properties of these tissues are qualitatively similar. It focuses on arteries. As a material, arteries are inelastic. They do not meet the definition of an elastic body, which requires that there should be a single-valued relationship between stress and strain. Arteries show hysteresis when they are subjected to cyclic loading and unloading. When held at a constant strain, they show stress relaxation. When held at a constant stress, they show creep. They are anisotropic. Their stress-strain-history relationships are non-linear. Their properties vary with the sites along the arterial tree, ageing, short- or long-term effects of drugs, hypertension, and inervation or denervation. An approach to non-linear elasticity uses the incremental law: a linearized relationship between the incremental stresses and strains obtained by subjecting a material to a small perturbation about a condition of equilibrium.