Upper bound limit analysis method is applied to determine the required reinforcement for three-dimensional stability of the slopes under seismic conditions. Horizontal blocks are used for determining the internal stability in three dimensional conditions. Seismic stability is studied by adopting a pseudo-static approach, considering only the horizontal acceleration. Reinforced soil has been considered to be a cohesionless material in the analysis. The failure mechanism is considered to be transitional and consists of several horizontal hexagonal blocks and a pentagonal one at the base. Velocity discontinuities between blocks are considered to be horizontal and each block consists of one reinforcement layer. Results are presented in graphical and tabular form to illustrate the effects of variation of different parameters such as seismic acceleration, three-dimensional geometry of the slope and soil friction angle on required reinforcement length and strength. By increasing of seismic acceleration, the stability of the reinforced soil slope decreases significantly, and thus greater strength and length of the reinforcement are required to maintain stability of the slope. On the other hand, three-dimensional modeling of reinforced slope results lower values of the required reinforcement. Comparisons of the present results with available pseudo-static results are shown, and discussed.

Statement of Problem: Disinfection of dental impressions is a weak point in the dental hygiene chain. In addition, dental office personnel and dental technicians are endangered by cross-contamination.Objectives: This study aimed to investigate the dimensional stability of two color-changing irreversible hydrocolloid materials (IH) after disinfection with glutaraldehyde.Materials and Methods: In this in vitro study, impressions were made of a master maxillary arch containing three reference inserts on the occlucal surface of the left and right maxillary second molars and in the incisal surface of the maxillary central incisors. Two types of color-changing irreversible hydrocolloid (tetrachrom, cavex) were used. Glutaraldehyde 2% was used in two methods of spraying and immersion to disinfect the impressions. The control group was not disinfected. Casts were made of type IV gypsum. The linear dimensional change of the stone casts was measured with a profile projector. For statistical analysis, Kruskall-Wallis and Mann-Witney tests were used (a=0.05).Results: By immersion method, the casts fabricated from tetrachrom were 0.36% larger in the anteroposterior (AP) and 0.05% smaller in cross arch (CA) dimensions; however, the casts prepared after spraying of tetrachrom were 0.44% larger in the AP and 0.10% smaller in CA dimensions. The casts made from Cavex were 0.05% smaller in the AP and 0.02% smaller in CA dimensions after spraying and 0.01% smaller in the AP and 0.003% smaller in CA dimensions after immersion. Generally there were not significant differences in AP and CA dimensions of the experimental groups compared to the control (p>0.05).Conclusions: Disinfection of the tested color-changing irreversible hydrocolloids by glutaraldahyde 2% did not compromise the accuracy of the obtained casts.

Although some 3D slope stability algorithms have been proposed in recent three decades, still role of pore pressures in three dimensional slope stability analyses and considering the effects of pore water pressure in 3D slope stability studies needs to be investigated. In this paper, a limit analysis formulation for investigation of role of the pore water pressure in three dimensional slope stability problems is presented. A rigid-block translational collapse mechanism is used, with energy dissipation taking place along planar velocity discontinuities. Results are compared with those obtained by others. It was found that water pressure causes the three-dimensional effects to be more significant, especially in gentle slopes. This may be related to the larger volume of the failure mass in gentle slopes resulting in more end effects. Dimensionless stability factors for three dimensional slope stability analyses are presented- including the 3D effect of the pore water pressure- for different values of the slope angle in cohesive and noncohesive soils.

This paper deals with three-dimensional evaluation of the slopes on the basis of limit analysis. An upper-bound technique of limit analysis is used in this paper to determine either the bearing capacity of a shallow foundation near a slope or the safety factor of the slope. The theorems of limit analysis (upper and lower bound) provide a powerful tool for solving problems in which limit loads need to be found. According to the upper-bound theorem, for a kinematically admissible velocity field an upper bound of the collapse load can be obtained by equating the power dissipated internally in an increment of displacement to the power expended by the external loads. Such kinematically admissible velocity fields have to comply with the kinematical boundary conditions and compatibility conditions. A rotational mechanism consisting of three slip surfaces is used to determine the factor of safety for a slope or the ultimate limit load of a foundation with eccentric load near a slope. This mechanism includes two lateral surfaces and a surface at bottom. As the soil is assumed to obey the associated flow rule, the angle between the relative velocity vector and velocity discontinuity has to be equal everywhere with soil's friction angle (j).The geometries of lateral surfaces are represented by a nonlinear differential equation. A surface with log-spiral section is used for bottom surface of the mechanism. To obtain the minimum upper-bound, an algorithm is proposed to optimize the failure mechanism. Results from this algorithm for typical conditions are comparable to those of other existing methods. Dimensionless diagrams for various conditions are presented which can be used to predict the bearing capacity of a foundation with eccentric load located on a slope.

A three-dimensional slope stability method based on limit analysis is proposed to investigate the pore water pressure effects. A rigid-block translational collapse mechanism is considered, with energy dissipation taking place along planar velocity discontinuities. The failure mass is assumed to be symmetrical and homogeneous. The approach can be considered as the modification and extension of the procedure proposed by Farzaneh and Askari in. Results are compared with those obtained by other researchers in two and three dimensional cases.

A theoretical study analyzing three-dimensional combustion acoustic instabilities in a liquid propellant rocket engine combustor has been conducted. A linear theory based on Crocco's pressure sensitive time lag model is used. To apply this theory, the combustor is divided into two main components, including the combustion chamber and the converging part of the nozzle. The assumption of concentrated combustion zone is used and the governing perturbation equations describing oscillations of flow variables are considered. To solve these equations appropriate boundary conditions at both ends of the combustion chamber are req1lired. Combustion zone boundary condition at one end and the nozzle admittance relation at other end are used. To obtain the nozzle admittance the three dimensional flow perturbation equations are solved in the converging part of the nozzle. This approach is capable of predicting acoustic stability behavior of a combustor at a wide range of Mach numbers and frequencies. Also, this analysis enables the rocket engine designer to observe the effects of different parameters such as nozzle entrance Mach number, chamber geometry, nozzle geometry. and gas properties on stability characteristics of an engine combustor. In case of instability observation; one can predict the acoustic mode which causes the instability and achieve an optimum design before conducting any expensive and time consuming experimental tests. This paper presents the stability analysis results and a parametric study of the effect of design parameters on stability characteristics of a typical combustor.

Presented is a rigorous solution for the three-dimensional stability analysis of convex slopes with corners in plan view. The method is based on the upper-bound theorem of limit analysis approach. A rigid-block translational collapse mechanism is considered, with energy dissipation taking place along planar velocity discontinuities. This mechanism is optimized to obtain the minimum factor of safety for stability of the corners. The algorithm can also be used to determine the ultimate limit load of a foundation located on a corner. Based on comparisons with known solutions, the method was generally found to be accurate in predicting the stability of such slopes. The numerical results indicate that the unloaded corners are more stable than the straight slopes. Dimensionless diagrams for various corner angles are also presented.

Influences of the wood fiber acetylation as well as the compatibilizer MAPP on water absorption, thickness swelling and dimensional stability of acetylated wood/ polypropylene composites (WPCs) were the main concerns of this research. Wood fibers were acetylated with acetic anhydride without using any catalyst to achieve weight percent gains (WPGs) of 4.5, 7.5 and 17.6%. The acetylated fibers were mixed with MAPP (0, 2, 3 and 5%) and matrix polymer polypropylene (PP) to prepare samples of the WPCs. The samples were made at 180°C with a hot press. Tests specimens were cut and soaked in the water for 1512 hours to determine the water absorption, the thickness swelling, the anti-swelling as well as the water repellent effects in the acetylated WPCs. The interfaces between acetylated wood fibers and the polypropylene were studied with a scanning electron microscope. Results revealed that acetylation of the wood fibers reduced significantly the water absorption and the thickness swelling in the WPCs. Addition of the MAPP decreased those properties as well. However, influence of the fiber acetylation was more effective than that of the MAPP. Electron microscopy of the interfaces showed reduction of micro-gaps in the WPCs and also improved interfaces between matrix polymer (PP) and the wood fiber. It was also revealed that the acetylated WPCs had smooth surfaces.

Statement of problem: The accuracy and dimensional stability of dental impression materials and technique is an important factor in the accuracy and fitness of the final restoration. Condensation- reaction polysilicone impression material has adequate accuracy and is the most commonly used material in fixed prosthodontic restorations with putty- wash technique. There are different considerations and controversies in the literature about the effect of impression technique on the accuracy of restoration.Purpose: The aim of this study was to compare the accuracy and dimensional stability of two polysiloxane putty- wash impression techniques with and without spacer.Materials and Method: A laboratory model with two metallic dies was used. In one of the dies a horizontal notch was applied as an undercut. Ten impressions were made without spacer and another ten with spacer.Twenty stone models were made from both techniques. Dimensions of the stone models were measured and comparison was made with the laboratory model dimensions. The results were analyzed using T- test.Results: The results showed that the height of the dies without undercut was decreased in both groups, being significant in non- spacer technique (p<0.001). The distance between the two dies increased in both techniques. The difference was significant in technique without spacer (p<0.002). The height of the dies above the undercut increased and in both techniques they proved to be statistically significant (without spacer p<0.003 and with spacer p<0.001).Conclusion: The polysiloxane putty- wash impression technique with spacer is more accurate for fabricating the stone die.