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Conveniently sized sections from six removable partial denture castings were examined metallographically for porosity. Abrupt changes in cross sectional areas were the site of porosity in some specimens; also seen were small generalized areas of porosity unlikely to be disclosed radiographically.
For wave propagation at low frequencies in a porous medium, the Gassmann-Domenico relations are well-established for homogeneous partial saturation by a liquid. They provide the correct relations for seismic velocities in terms of constituent bulk and shear moduli, solid and fluid densities, porosity and saturation. It has not been possible, however, to invert these relations easily to determine porosity and saturation when the seismic velocities are known. Also, the state (or distribution) of saturation, i.e., whether or not liquid and gas are homogeneously mixed in the pore space, is another important variable for reservoir evaluation. A reliable ability to determine the state of saturation from velocity data continues to be problematic. It is shown how transforming compressional and shear wave velocity data to the (rho/lambda, mu/lambda)-plane (where lambda and mu are the Lame parameters and rho is the total density) results in a set of quasi-orthogonal coordinates for porosity and liquid saturation that greatly aids in the interpretation of seismic data for the physical parameters of most interest. A second transformation of the same data then permits isolation of the liquid saturation value, and also provides some direct information about the state of saturation. By thus replotting the data in the (lambda/mu, rho/mu)-plane, inferences can be made concerning the degree of patchy (inhomogeneous) versus homogeneous saturation that is present in the region of the medium sampled by the data. Our examples include igneous and sedimentary rocks, as well as man-made porous materials. These results have potential applications in various areas of interest, including petroleum exploration and reservoir characterization, geothermal resource evaluation, environmental restoration monitoring, and geotechnical site characterization.
Some landslides move imperceptibly downslope, whereas others accelerate catastrophically. Experimental landslides triggered by rising pore water pressure moved at sharply contrasting rates due to small differences in initial porosity. Wet sandy soil with porosity of about 0.5 contracted during slope failure, partially liquefied, and accelerated within 1 second to speeds over 1 meter per second. The same soil with porosity of about 0.4 dilated during failure and slipped episodically at rates averaging 0.002 meter per second. Repeated slip episodes were induced by gradually rising pore water pressure and were arrested by pore dilation and attendant pore pressure decline.
Bioresorbable bone graft substitutes could eliminate disadvantages associated with the use of autografts, allografts and other synthetic materials. We investigated a bioresorbable bone graft substitute made from the unsaturated polyester poly(propylene fumarate) which is crosslinked in the presence of soluble and insoluble calcium filler salts. This compact bone graft substitute material develops porosity in vivo by leaching of the soluble filler salts. In attempt to develop materials whose in vivo porosity can be designed such that implant degradation would occur at a rate that remains supportive of the overall structural integrity of the repairing defect site, we studied the early tissue response upon implantation in a bony defect. Three grout formulations of varying solubilities using slightly soluble hydroxyapatite (HA) and soluble calcium acetate (CA) were evaluated in 3 mm holes made in the anteromedial tibial metaphysis of 200 g Sprague Dawley rats (n = 16 per formulation for a total of 48 animals). Grout formulations cured in situ. Animals from each formulation were sacrificed in groups of 8 at 4 days and 3 weeks postoperatively. Histologic analysis of the healing process revealed improved in vivo osteointegration of bone graft substitutes when a higher loading of calcium acetate was employed. All formulations maintained implant integrity and did not provoke sustained inflammatory responses. This study suggested that the presence of a soluble salt permits in vivo development of porosity of a poly(propylene fumarate) based bone graft substitute material.
We investigated four acrylic cement preparation techniques for their effects on cement porosity: hand mixing, pressurization in a pneumatic pistol, centrifugation, and vacuum mixing. All the techniques were tested on three types of cement with different viscosity characteristics. The best results were obtained with vacuum mixing using a newly designed experimental system, yielding porosity reductions of 60-80 percent relative to hand mixing. Vacuum mixing with a commercial system was also effective, but to a somewhat lesser extent. Pressurization and centrifugation had no substantial effect on the overall porosity. Centrifugation led to considerable nonuniformity in the distribution of pores and additives.
BACKGROUND: We developed a new fibronectin bonding to expanded polytetrafluoroethylene (ePTFE) and previously reported that, in a dog carotid implant model, fibronectin bonding improves graft healing in high porosity ePTFE grafts. The purpose of this study was to further investigate the effect of the fibronectin bonding on graft healing in a pig carotid implant model. METHODS: Fifteen pigs received a high porosity ePTFE graft treated with the fibronectin bonding (fibronectin-bonded graft) on one side and an untreated graft (non-bonded graft) on the contralateral side. The grafts were explanted at intervals of 3 and 6 weeks and subjected to histological studies. RESULTS: At 3 weeks, the neointima of fibronectin-bonded grafts was better organized than that of non-bonded grafts. At 6 weeks, the morphologic features of the neointima were the same in fibronectin-bonded and non-bonded grafts. The neointima was completely organized. CONCLUSIONS: Together with the previous results with the dog model, fibronectin bonding could be expected to improve healing of the high porosity ePTFE grafts in humans.
This paper reports on the influence of the material porosity on the anaerobic biomass adhesion on four different inert matrices: polyurethane foam, PVC, refractory brick and special ceramic. The biofilm development was performed in a fixed-bed anaerobic reactor containing all the support materials and fed with a synthetic wastewater containing protein, lipids and carbohydrates. The data obtained from microscopic analysis and kinetic assays indicated that the material porosity has a crucial importance in the retention of the anaerobic biomass. The polyurethane foam particles and the special ceramic were found to present better retentive properties than the PVC and the refractory brick. The large specific surface area, directly related to material porosity, is fundamental to provide a large amount of attached biomass. However, different supports can provide specific conditions for the adherence of distinct microorganism types. The microbiological exams revealed a distinction in the support colonization. A predominance of methanogenic archaeas resembling Methanosaeta was observed both in the refractory brick and the special ceramic. Methanosarcina-like microorganisms were predominant in the PVC and the polyurethane foam matrices.
Secondary forest is the main body of forests in China, and hence, its management plays a very important role in the projects of natural forest conservation and ecological environment construction in this country. The structure, especially the vertical stratification structure of secondary forest is one of the key factors in the management of secondary forest, and can be considered as the base of its management. Based on previous studies, the concept of stratification porosity was introduced, and the optical stratification porosity (OSP), which is the two dimensional alternative measurement of stratification porosity, could be used to represent the vertical stratification structure of secondary forest. The method using hemispherical photographic silhouette (photographic silhouette taken with fisheye lens) to estimate the OSP of a forest stand was also introduced. In addition, the possible applications of OSP in studies on the structure and restoration ecology of secondary forest, and the theory and techniques for the management of secondary forest were also given in this paper.
The aim of this study was to determine the influence of the nature of the perigraft tissue in the healing pattern of high-porosity polytetrafluoroethylene (PTFE) vascular grafts. Nine-centimeter long segments of unreinforced experimental high-porosity (60 microns) PTFE grafts were placed as abdominal aortic interposition in mongrel dogs. Three grafts served as controls (group A); in five dogs (group B) a 25 x 25 cm piece of devascularized omentum was wrapped around the graft. In five dogs (group C) the omentum with its own vascular supply was completely wrapped around the graft. Animals were killed 4 weeks after surgery. The percentage of thrombus-free area was 31% in group A grafts, 39% in group B grafts, and 79% in group C grafts (p less than 0.01). Scanning electron microscopy showed many confluent areas of endothelium-like cells in the midportion of group C grafts, corresponding to capillary ingrowth. Transmural endothelial migration was more evident in group C grafts. We conclude that the nature of the perigraft tissue influences transmural capillary migration and the endothelialization rate of high-porosity PTFE grafts in dogs. Agents able to increase capillary formation in the perigraft tissue might improve endothelialization of vascular grafts.
The porosity and the mechanical strength of 64 bone cement specimens were investigated. Different types of mixing procedures were tested: 1) hand, 2) compression, 3) vacuum and 4) the combination of vacuum stirring and compression. The differences in porosity and mechanical stability are remarkable. In relation to hand-mixed bone cement all techniques are leading to a reduction in the number of cavities. Specimens made by compression are showing a confluence of several small cavities to a few large. There is only a change in the distribution of the embedded gas volume, but not a reduction. The lowest porosity is seen in vacuum mixed specimens.
The porosity of composite materials was investigated. For the 5 materials tested the values varied between 5.9 and 2.2 vol. %. The volume of porosity could be reduced markedly by a short application of pressure upon the mixed material. Pressure and time of pressure were checked separately, and it could be shown that the percentage of porosity reduction was correlated almost completely with the viscosity of the composite.
Intraoperative investigations after axillary thoracotomy in 28 patients with spontaneous pneumothorax shows true ruptures of subpleural bullae in 25% of the cases. In 75% structural pleural changes in the top of the lung are responsible for porosity and air leakage of the wall of the bullae. Pleural porosity causes a prolonged treatment of this illness. Appreciation of the phenomenon of "pleural porosity" is the key for understanding several questions regarding the diagnosis and treatment of spontaneous pneumothorax that had remained unanswered to date.
The strength and hardness of dental stone were found to have better a correlation with porosity than with water-powder ratio. Within the range of porosity of less than 34 vol-%, the strength and hardness varied logarythmically with a linear change in porosity.
Nicotine was fed to rats for 6 weeks, as a weight adjusted dose equivalent to that of a human being smoking 50 to 100 cigarettes per day. Those rats fed nicotine developed hypercholesterolaemia. Scanning electron microscopy showed the porosity of the hepatic sinusoidal endothelium of nicotine fed animals was about 40% that of control animals. The decline in porosity was found to be due to a reduction in diameter rather than number of fenestrae. We believe that this decreased hepatic sinusoidal porosity may alter cholesterol homeostasis by increasing the circulation time of chylomicron remnants too large to pass through the fenestrae. This phenomenon may be an aetiological factor in the known correlation between cigarette smoking, atherosclerosis, and coronary heart disease in humans.
The influence of the porosity on the fate of the neointima of E-PTFE grafts implanted to the canine abdominal aorta was experimentally investigated. E-PTFE grafts (each 7 cm X 8 mm) which were pretreated with multiple regular small perforations using a needle were divided into 4 groups according to the mode of the perforation; in Group A perforations were made at regular 2 mm interval with 21 gauge needle, in Group B at 2 mm interval with 25 gauge needle and in Group C at 4 mm interval with 25 gauge needle, in Group D at 4 mm interval with 27 gauge needle, respectively. The grafts in Groups A and B revealed the infiltration of the fibroblasts and development of vasa vasorum from outside to inside through the perforated holes 14 days after implantation, and then the neointimatization of the grafts was completed 180 days after implantation. The grafts in Groups C and D demonstrated incomplete healing of the central luminal portion of the graft even 180 days after implantation. In contrast, Untreated E-PTFE grafts showed little neointimatization and luminal surface of the graft was mostly covered with mural thrombi 180 days after implantation. The study demonstrated that the porosity of E-PTFE graft is insufficient in early neointimatization, while increasing the porosity with multiple small perforations plays a significant role in early development of neointima.
A controlled study of the relationship of two standard clinical indicators of osteoarthritis and porosity failed to demonstrate a relationship. Porosity appears to be a curiosity that has no clinical correlation and is not a sign of an identifiable rheumatologic disorder. It should be deleted as an identifier for osteoarthritis.
The aim of this study was to investigate the effect of adding an elastomeric second phase, acrylonitrile-butadiene-styrene, on the fatigue crack propagation behavior of poly(methyl methacrylate) bone cement. Moreover, the influence of porosity and environmental conditions was studied. When comparing the plain cement to the modified cement, a decrease in the crack propagation rate was observed at between 1 and 2 orders of magnitude. The storage in a physiological environment (saline solution at 37 degrees C) also caused a decrease in the crack propagation rate of about 2 orders of magnitude for the plain and modified cement prepared in air or under a vacuum. Porosity did not have any noticeable effect on the fatigue crack propagation behavior of the cement.
The influence of the storage temperature of the cement constituents prior to mixing (21 vs. 4 degrees C) and the mixing method (hand mixing vs. vacuum mixing) on the uniaxial tension-compression fatigue performance and porosity of Palacos R acrylic bone cement was studied. The fatigue results were analyzed using the three-parameter Weibull equation. The fatigue performance was expressed as an index I, which was defined as the product of the Weibull characteristic fatigue life and the square root of the Weibull slope. Statistical analyses of these results show that although the mixing method (for a given storage temperature) exerts a significant influence on the fatigue performance and areal porosity, the effect of storage temperature (for a given mixing method) on either of these parameters is not significant.