Dilatancy Relationship Research Articles

The initiation of flow in granular materials

The effects of rotation of principle stress directions on the initiation of flow in particulate materials have been studied experimentally in the Directional Shear Cell. Four materials were tested: sand, coal, kaolinite and bentonite. A range of dampness from dry to full saturation was covered. For sand and coal, the rotation of principal stress directions causes initiation of flow at much lower stress ratios than monotonic loading and the reduction is related to the amplitude of rotation. There were strong indications that similar effects exist in saturated and nearly saturated kaolin but further work is required. Two simple quantitative stress dilatancy relationships are related to basic mechanisms of energy dissipation and have been strongly confirmed in a wide range of experimental conditions. Monotonic shearing of granular material after shear under cyclic rotation of principal stress directions has shown large gains in shear strength and stiffness which are not related to any density change under cyclic loading.

Fine structure of hepatic sinusoids and sinusoidal cells in disease

Liver sinusoids are special capillaries that are limited by fenestrated endothelial cells, without a genuine basement membrane, surrounded by perisinusoidal cells storing vitamin A, and harbouring Kupffer cells and pit cells, resident macrophages, and large granular lymphocytes, respectively. Each nonparenchymal cell and parenchymal cell of the liver interacts with all others and with the extracellular matrix. Therefore, the functional ability of each cell is constantly being modified by the metabolic activity of the others. Human liver biopsies (132), needle or surgical, perfusion-fixed with glutaraldehyde and processed for transmission electron microscopy (TEM), and occasionally for scanning electron microscopy (SEM), were examined. The study included liver diseases (such as alcoholic liver diseases, benign and malignant liver tumors, cholestasis of various origins, fulminant hepatitis, acute rejection after orthotopic liver transplantation, Budd-Chiari syndrome), as well as general or extrahepatic diseases (such as diabetes, hemochromatosis, hypervitaminosis A, various hematological disorders), and normal controls. Ultrastructural abnormalities are described and illustrated under two different headings: 1) elementary lesions of sinusoidal cells (endothelial, Kupffer, perisinusoidal and pit cells), nonsinusoidal cells (in the space of Disse and/or in the lumen), the extracellular matrix; and 2) the major pathological entities including perisinusoidal fibrosis, capillarization of sinusoids, sinusoidal dilatation, and peliosis. In the discussion, an overview of the major abnormalities reported in the literature is presented, and some specific questions regarding 1) perisinusoidal fibrosis in liver with normal histology, 2) the overload of perisinusoidal cells with lipids in non-hypervitaminosis A intoxication and 3) the etiological relationship of sinusoidal dilatation, peliosis, perisinusoidal fibrosis, or sinusoidal tumors with drugs and toxic compounds are discussed. In the event that lesions are not specific to any diagnosis, the knowledge of the ultrastructure of sinusoids is extremely useful from the perspective of the liver as an ecosystem.

Stress Dilatancy of Sand at Small Stress Ratio States

The validity of the stress dilatancy equation for representing the small stress ratio state response of sand is examined. Test equipment development and procedures that were followed aimed at precise loading control and reliable monitoring of small displacements and volume changes. A variety of load controlled stress paths were applied to conventional triaxial test samples of Ottawa sand. The results obtained show that at small stress ratio states a relationship between stress state and strain increment direction as prescribed by the stress dilatancy equation does not apply. Stress increment directions were found to be related to strain increment directions for low stress ratio states. The relationship has some resemblance to the behavior of a cross anisotropic elastic material with a stiffer vertical to radial response. The range of low stress ratio states over which a stress dilatancy relationship does not apply tends to increase with density. In stress ratio regions where the stress dilatancy equation began to apply, the relationship between R and D tends toward KCv with increasing confining stress for conventional triaxial but not for constant mean normal stress paths.

The relationship between hypertrophy and dilatation in the postmortem heart.

Confusion may exist at the time of postmortem examination as to whether the diseased heart is dilated, hypertrophied, or both. Ventricular dilatation and ventricular hypertrophy were therefore evaluated by cardiac partition techniques in 441 subjects at autopsy to determine their relationship. Specific weight and surface area of each ventricle were obtained and patients were divided into categories of disease. Wall thickness measurements, a parameter routinely used in the ordinary autopsy, were found to be unreliable in defining hypertrophy. Ventricular surface area (an index of dilatation) was highly correlated with ventricular weight in most disease categories. Exceptions were cardiomyopathy and aortic stenosis, in which hypertrophy predominated. We conclude from these data that dilatation and hypertrophy occur proportionately in the postmortem heart in most disease categories except in cardiomyopathy and aortic stenosis. These findings clarify the relationship of dilatation and hypertrophy at the time of autopsy in most cases. Therefore, uncertainty as to whether cardiac dilatation or hypertrophy is present or which predominates is usually related to the inability to assess these states critically at the time of autopsy when the ordinary pathological methods are used.

Temperature relationship of concentration dilatation and specific capacity of hydrogen diffusion filters of V-1 alloy

This paper investigates the temperature relationship of concentration dilatation and specific capacity of tubular diffusion elements of V-1 alloy in a wider temperature range than has been done until now on thick flat specimens. The specific capacity was measured in parallel with nonequilibrium concentration dilatation, with determination of the elongation of the tubular filter caused by occluded hydrogen in the diffusion flow and by the concentration gradient of hydrogen across the filter thickness. In individual experiments, data was obtained on the equilibrium concentration dilatation of the same 2.5/2.3-mm-diam. tubular specimens of V-1 alloy.

Dependence of the compaction of vitreous silica on the ionization dose

Earlier data for the relationship of negative dilatation of vitreous silica to the ionization dose of 0.3 and 0.6-MeV electrons are clarified and corrected. Values are given for the maximum and the mean dilatations along the electron path in the material.

Effect of stimulus uncertainty on the pupillary dilation response and the vertex evoked potential

Scalp recordings of slow baseline shifts (CNV) preceding auditory stimuli, as well as pupillary dilations and evoked potentials to these stimuli, were recorded and averaged in awake adult humans. The experimental situation manipulated the degree of advance knowledge by the subject as to which of two auditory stimuli would be presented next. In the certain condition the subject was told prior to each stimulus which of the two stimuli would be presented next; in the uncertain condition the subject made a guess prior to each stimulus and the occurrence of the stimulus confirmed or disconfirmed the subject's guess. In both the certain and uncertain conditions, the relative probability of occurrence of the two stimuli was varied in different blocks of trials so that each of the two stimuli occurred at 20, 40, 60 and 80% probabilities. Pupillary dilation was found to be larger and the CNV was found to be more negative in the uncertain condition than in the certain condition. Of the evoked potential components, P 3 was larger and N 2 was smaller in the uncertain condition. Somewhat less consistently, P 2 was larger and P 1 and N 1 were smaller in the uncertain condition. P 3 amplitude and peak dilation amplitude decreased monotonically as a function of the rareness of event occurrence (as measured by either stimulus or outcome probability). This relationship held for P 3 in both certain and uncertain conditions, but only in the uncertain condition for pupillary dilation. The P 2 component also showed similar relationships to probability, but less strongly than did the P 3 component. CNV did not vary as a function of stimulus probability in either condition. The results are consistent with the interpretation that the uncertain condition is characterized by a higher arousal level associated with greater task involvement on the part of the subject. The similarity between the pupillary dilation relationship to probability and the P 3 relationship to probability is consistent with an interpretation of P 3 as a “cerebral correlate of the orienting response”. But this would require a broadening and redefinition of the orienting response concept in “informational” terms and in any case would fit all the available data on P 3 only with difficulty. A less ambitious formulation at this time would simply suggest that any operation which increases the “salience” of the stimulus to the subject tends to increase the amplitude of P 3.

Governing equations of plastic deformation of a granular medium: PMM vol. 35, n≗6, 1971, pp. 1070–1082

Linear tensor relationships between the stresses and strain rates in an isotropic plastic material contain two independent scalar functions. It is proposed to utilize two independent limit conditions to determine them: One is formulated in stress space (one of the forms of the Coulomb condition), and the other in the strain rate space (dilatancy relationship). Work-hardening is taken into account, the problem of the shear strain of a layer of sand is examined, the proposed governing equations are discussed comparatively. For simplicity, the analysis is restricted to plane motion.