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Unreliable resources in conventional power systems have created new challenges for the users of these systems. These sources of production, including wind and solar sources, with a significant share in the power generation of many power systems, cause problems in the safe and stable operation of power systems due to uncertainty. Therefore, it is very important to provide a method or model for safe and stable operation of power systems. The main innovation of this paper is to present a new SCUC model to maximize the flexibility of the system along with reducing the operating cost in the form of a security constrained multi-level robust optimization problem in the presence of wind uncertainty sources. Also, a set of demand response programs and rapid response hybrid cycle units are used as sources of flexibility. Accordingly, the tolerable range of uncertainty and system slope reservation is developed with a low-cost combination and with the commitment to flexible covering resources. The desired optimization problem has been solved with the help of the NCCG algorithm and MILP method. The efficiency and reliability of this proposed model have been simulated and evaluated in IEEE 6-bus and 118-bus standard power systems, and the simulation results confirm the technical and economic efficiency of this model. [ABSTRACT FROM AUTHOR]

Background: Hypodontia or congenitally missing teeth is among dental anomalies with different prevalence in each region. The aim of this study was to evaluate the prevalence of congenitally missing permanent teeth in Iranian population. Materials and Methods: A descriptive, retrospective and cross‑sectional study was done. Panoramic radiographs of 2422 Iranian patients (1539 girls and 883 boys), 7‑25 years old, were collected. The radiographs were studied for evidence of congenitally missing teeth. Data were analyzed using Paired t‑test, Mann‑Whitney test, Fisher exact test and Chi‑square test (α = 0.05). Results: Prevalence of congenitally missing teeth was totally 45.7% and 34.8% for third molars. The most frequent congenitally missing teeth was mandibular second premolars (23.34%) followed by maxillary second premolars (22.02%). Upper jaw showed significantly higher number of congenitally missing teeth (P value < 0.001). According to Chi‑square test, congenital missing teeth was found approximately 10.9% in both females and males and there were no statistically significant difference between sexes (P = 0.19). Conclusion: The prevalence of congenitally missing teeth (CMT) in Iranian permanent dentition was 10.9%. The most common congenitally missing teeth were mandibular second premolar fallowed by maxillary second premolars. [ABSTRACT FROM AUTHOR]

Introduction: Selection of appropriately-sized central teeth has an important role in esthetics of dentures. The aim of this study was to compare proportion of mesiodistal width of central incisors in the maxilla to those in the mandible in students and products of Idealmako Company. Materials and Methods: In this descriptive-analytical study, 93 students of Isfahan Faculty of Dentistry in the age range of 20-30 were selected randomly. Mesiodistal widths of left and right upper and lower centrals were recorded by two methods: directly, using an intraoral caliper, and indirectly, using subjects' casts and a caliper with an accuracy of 0.01 mm at height of counter of the teeth three times. The sizes of Idealmako products were measured by the same caliper. Data was analyzed by one-way ANOVA, t-test and post hoc Scheffé's test using SPSS software (α = 0.05). Results: Proportion of upper-to-lower mesiodistal width of centrals was 1.55 ± 0.13 in students and 1.68 ± 0.17 in Idealmako products. Conclusion: Mean proportion of mesiodistal width of upper centrals to lower centrals in natural teeth is less than that in artificial teeth. A similarity between the width of upper centrals in the natural and artificial teeth (the numerator of the fraction) accounts for this significant difference between the proportion of the two groups, leading to the very small size of lower centrals (denominator of the fraction) in Idealmako artificial teeth. [ABSTRACT FROM AUTHOR]

Fundamental principles of the X-ray diffraction of mesomorphic materials are discussed at length, especially for petroleum asphaltenes. Stepwise procedures for handling X-ray diffraction laboratory data are presented. [ABSTRACT FROM PUBLISHER]