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Cellular learning automata (CLAs) are learning models that bring together the computational power of cellular automata and also the learning capability of learning automata in unknown environments. CLAs can be open or closed. In a closed CLA , the action of each learning automaton depends on the neighboring cells, whereas in an open CLA , the action of each learning automaton depends on the neighboring cells, and a global environment. These models can be synchronous or asynchronous . In a synchronous CLA , all cells are activated at the same time, but in an asynchronous CLA , at a given time only some cells are activated. These models can be also static or dynamic . In a dynamic CLA, one of its aspects such as structure, local rule or neighborhood may vary with time . All existing dynamic models of the CLAs are closed. In this paper, an open asynchronous dynamic CLA has been introduced. In order to show the potential of this model, an algorithm based on this model for solving allocation hub location problem with imprecise distances among nodes has been designed. To evaluate the proposed algorithm computer simulations have been conducted. The results of simulations show that the proposed algorithm is more robust to imprecise distances as compared to existing algorithms. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: The aim of this study was to evaluate the effect of a range of alkaline pH values on the push-out strength of white mineral trioxide aggregate (WMTA). Methods: The standardized lumens of root slices prepared from extracted single-rooted human teeth were filled with white ProRoot MTA. The specimens were then randomly divided into 4 groups (n = 20) and wrapped in pieces of gauze soaked in synthetic tissue fluid (STF) (pH, 7.4) and STF buffered in potassium hydroxide at pH values of 8.4, 9.4, or 10.4. The samples were incubated for 3 days at 37°C. The push-out bond strengths were then measured by using a universal testing machine. Failure modes after the push-out test were examined under a light microscope at ×40 magnification. The data were analyzed by using one-way analysis of variance and Tukey post hoc tests. Results: The greatest (9.46 ± 0.63 MPa) and lowest (5.68 ± 0.83 MPa) mean push-out bond strengths were observed after exposure to pH values of 8.4 and 10.4, respectively. There were significant differences between the groups (P = .001). The bond failure was adhesive for all experimental groups. Conclusions: Push-out bond strength of WMTA could be influenced by different alkaline pH values. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: Storage temperature influences the properties of Portland cement during mixing. Because of similarities between Portland cement and mineral trioxide aggregate, the aim of the present study was to evaluate surface microhardness, topography, and phase structure of white mineral trioxide aggregate (WMTA) after storage in a range of temperatures. Methods: Thirty WMTA sachets were divided into 3 groups of 10. The 3 groups were stored at 4°C, 25°C, and 40°C for 48 hours with accompanying ampules. Sachets were immediately mixed after removal from storage according to manufacturer''s instructions and mixed and packed into cylindrical glass tubes at room temperature. Surface microhardness of each specimen was measured after 3 days. Four specimens from each group were prepared and observed under scanning electron microscope and x-ray diffraction. Data were subjected to one-way analysis of variance and a post hoc Tukey test at P <.05. Results: Mean surface hardness ± standard deviation after storage at 4°C, 25°C, and 40°C were 25.23 ± 5.99, 53.56 ± 3.28, and 62.89 ± 1.76, respectively. Statistically significant differences were observed among the groups (P < .001). More voids and a disorganized, flake-like topography were observed in specimens stored at 4°C in comparison with those stored at 25°C and 40°C. X-ray diffraction meter generated similar peaks at 40°C and 25°C, but slight differences were observed at 4°C. Conclusions: This study indicated that storage temperature might influence surface hardness and microstructure of WMTA. [Copyright &y& Elsevier]

Abstract: Introduction: The aim of this study was to evaluate morphologic microstructure and surface hardness of white mineral trioxide aggregate (WMTA) after exposure to a range of alkaline environments during hydration. Methods: WMTA was mixed and packed into 60 glass tubes. Four groups, each containing 15 tubes, were exposed to pH values of 7.4, 8.4, 9.4, and 10.4, respectively, for 3 days. In 12 tubes in each group, Vickers surface hardness was measured after exposure to alkaline environments. Data were subjected to one-way analysis of variance and a post hoc Tukey test. Three specimens in each group were prepared to be evaluated under a scanning electron microscope using scattered electron (SE) and backscattered electron (BSE) detectors. Results: The mean surface hardness values ± standard deviation after exposure to pH values of 7.4, 8.4, 9.4, and 10.4 were 58.28 ± 8.21, 68.84 ± 7.19, 67.32 ± 7.22, and 59.22 ± 9.14, respectively. The difference between these values was statistically significant (p = 0.000). There were statistically significant differences between pH values of 8.4 and 9.4 and pH values of 7.4 and 10.4 (p > 0.05). The SE detector revealed needle-shaped crystals at pH values of 7.4 and 8.4 and an amorphous microstructure at pH values of 9.4 and 10.4 on WMTA surface. The BSE detector showed more unhydrated structure and pores at pH values of 7.4 and 10.4 compared with pH values of 8.4 and 9.4. Conclusions: Surface hardness can be influenced by different alkaline pH values. The BSE detector can reveal more microstructure details of WMTA in conjunction with the SE detector. More porosity and unhydrated structure are observed in WMTA exposed to pH values of 7.4 and 10.4. [Copyright &y& Elsevier]

Abstract: The aim of the present study was to evaluate microleakage of mineral trioxide aggregate (MTA) used as a root-end filling material after its exposure to a range of acidic environments during hydration. Seventy single-rooted teeth were divided into 4 experimental and 2 control groups. All the teeth were instrumented, and their apices were resected. Root-end cavities were filled with white MTA in the experimental groups. In the control groups root-end cavities were not filled. Root-end fillings were exposed to acidic environments with pH values of 4.4, 5.4, 6.4, or 7.4 for 3 days in the experimental groups. Microleakage was evaluated by using bovine serum albumin. The evaluation was conducted at 24-hour intervals for 80 days. Data were analyzed by using one-way analysis of variance and a post hoc Tukey test. The earliest bovine serum albumin microleakage was observed in a pH value of 4.4 followed by pH values of 5.4, 6.4, and 7.4, respectively. There was a significantly longer time necessary for leakage to occur in samples stored in higher pH values (P < .000). [Copyright &y& Elsevier]

Objective: The aim of this study was to find a relation between erosion and microhardness of root canal dentin after irrigation with different canal irrigants. Study design: Seventy-two single-canal human premolar teeth were selected and enlarged by rotary Protaper files. The middle part of each root was transversely sectioned to a 4-mm slice. The initial microhardness values of intact specimens were measured at depths of 100 μm and 500 μm from the pulp-dentin interface using a Vickers microhardness tester. the specimens were divided into 6 groups of 12 specimens and were treated as follows: 1: 2.6% NaOCl, 2: 17% EDTA (5 minutes) then 2.6% NaOCl (5 minutes), 3: 17% EDTA (1 minute) then 2.6% NaOCl (1 minute), 4: MTAD (5 minutes), 5: 2% Chlorhexidine (5 minutes), and 6: saline (control), respectively. Posttreatment microhardness values were obtained in the same manner as the initial ones. Afterwards, the specimens were prepared for scanning electron microscopy analysis. The amount of dentin erosion was examined. Results: Group 2 showed the most erosive effect on dentin (P < .0001) along with the least decrease of dentin microhardness at depth of 100 μm, whereas MTAD showed the most reduction of dentin microhardness and less erosive effect on dentin. Conclusion: It can be concluded that erosion is not the main factor in decreasing the dentin microhardness, whereas the amount of irrigant penetration might be the main cause. [Copyright &y& Elsevier]