فهرست مطالب مهسا نجفی

The present paper presents an accurate and efficient method for the analysis of free vibration of piezoelectric nanobeam. In this method, Eringen's nonlocal elasticity theory is used to apply the small-scale effects. Despite the shear deformation theories, in the present theory, the displacement and strain fields are considered as a general form, and out-of-plane normal strain is not neglected. The governing equations of piezoelectric nanobeam are derived by employing Hamilton's principle. By solving these equations, natural frequencies related to flexural and thickness modes for the free vibration of nanobeam are obtained. The Convergence of the predicted results is studied, and the effects of various parameters such as nonlocal parameter, length to thickness ratio, and applied external voltage are investigated. To verify the accuracy of the present method, the results predicted by the present theory are compared with those of the theories available in the literature and the finite element method. This study shows that the natural frequencies predicted by the present theory are smaller than those of shear deformation theories. The results of this study show that the natural frequency of the piezoelectric nanobeam increases by increasing the negative applied electric voltage as well as tensile axial load and decreasing the nonlocal parameter. The results show that the natural frequencies related to thickness modes are not negligible and the shear deformation theories, the present theory can predict these frequencies.

Aging is a process over time that leads to negative structural and functional changes in the loss of adaptation and coordination both physically and mentally. An active lifestyle can minimize the progression of many debilitating conditions and chronic diseases, as well as help achieve aging and healthy well-being. The aim of the present study was to compare the cognitive triangle and mental health in the elderly living in nursing homes, homes and active elderly.

The present was causal-comparative. The statistical population consisted of the elderly (40 people from each group) living in a nursing home, living at home and an athlete in Malayer. 120 elderly were selected by convenience sampling method based on inclusion criteria. Data collection was performed using demographic questionnaires, cognition triangle and GHQ general health questionnaire. Multivariate analysis of variance and Tukey post hoc test were used to analyze the data.

Active elderly had significantly better scores of physical symptoms, anxiety and depression than the other two groups and the elderly living in the home group had better physical symptoms, anxiety and depression than the resident group of the nursing home. For the variable of social symptoms, there was a significant difference between the mean scores of the active elderly group and the elderly living in nursing homes (p <0.05). The active elderly had higher mean physical symptoms than the other two groups, There was no significant difference in nursing homes. There are significant pair differences between the scores of the cognitive triangle components of self-attitude, attitude towards the future and attitude towards the world in the groups of active elderly, home residents and nursing home residents (p <0.05). The active elderly had a significantly better score in the three components of the cognitive triangle than the other two groups and the elderly in the home group had a better score in the triangular components than the resident group in the nursing home.

Findings of this study show that physical activity helps to improve mental health and cognitive triangle, so to maintain mental and physical health of the elderly should be appropriate strategies.Introduction and

Aging is a process over time that leads to negative structural and functional changes in the loss of adaptation and coordination both physically and mentally. An active lifestyle can minimize the progression of many debilitating conditions and chronic diseases, as well as help achieve aging and healthy well-being. The aim of the present study was to compare the cognitive triangle and mental health in the elderly living in nursing homes, homes and active elderly.

The present was causal-comparative. The statistical population consisted of the elderly (40 people from each group) living in a nursing home, living at home and an athlete in Malayer. 120 elderly were selected by convenience sampling method based on inclusion criteria. Data collection was performed using demographic questionnaires, cognition triangle and GHQ general health questionnaire. Multivariate analysis of variance and Tukey post hoc test were used to analyze the data.

Active elderly had significantly better scores of physical symptoms, anxiety and depression than the other two groups and the elderly living in the home group had better physical symptoms, anxiety and depression than the resident group of the nursing home. For the variable of social symptoms, there was a significant difference between the mean scores of the active elderly group and the elderly living in nursing homes (p <0.05). The active elderly had higher mean physical symptoms than the other two groups, There was no significant difference in nursing homes. There are significant pair differences between the scores of the cognitive triangle components of self-attitude, attitude towards the future and attitude towards the world in the groups of active elderly, home residents and nursing home residents (p <0.05). The active elderly had a significantly better score in the three components of the cognitive triangle than the other two groups and the elderly in the home group had a better score in the triangular components than the resident group in the nursing home.

Findings of this study show that physical activity helps to improve mental health and cognitive triangle, so to maintain mental and physical health of the elderly should be appropriate strategies.

With increasing demand on esthetics in children andtheir parents,the treatment of decayed primary anterior teeth is oneof the biggest challenges in pediatric dentistry. Esthetic preformedzirconia crowns are the newest choice in treatment of the anterior aswell as the posterior teeth.

This paper reports a 3 years old boy with grosslydecayed maxillary incisors which was planned to treat under generalanesthesia. In this case,we used preformed zirconia crowns (NuSmile,Houston,TX,USA) to restore function,ideal esthetics in anteriorteeth. The patient was followed for two years for function,gingivalhealth,crown adaptation which were in good condition. The patientand their parents were completely satisfied with the crown appearance.

The preformed zirconia crown is durable,well-favoredchoice to restore primary anterior teeth.

Inroduction & Objective: The global assessment of animals provides amphibians are more threatened and declining more rapidly than either birds or mammals. The presence of alien or exotic species is an important factor in the decline or extinction of amphibian populations, which contribute to the decline of the amphibian population by hunting eggs and larvae. Also, it has been recognized in previous researches that refugia can be an effective way to protect amphibians against invasive species, including Mosquitofish. In this study, in order to investigate the effect of refugia on the survival of Bufovariabilis in the presence of Gambusiaaffinis, the independent and interactive effects of two factors of refugia type (including three treatments of absent, simple and complex refugia) and predator density (including three treatments of non-predator, one and three predators) carried out within 10 days. In this study, the highest survival rate was observed in the complexrefugia / non-predator with 96.66% ±17.10, and the lowest survival rate was observed in the absence of refugia / three predators (0%). In general,the results of ANOVA showed both predator density and refugia type had a significant effect on survival, but their interactive effect is not significant.Considering the effect of time, predator density independently showed a significant effect on the survival rate, but this effect is not significant for the type of refugiaand its interactive effect with predator density over time. The number of Green toad in the test environment, with suitable refugia, greatly decreases with increasing predator density.

Due to important rule of edge stresses in the delamination and local failure of laminated structures, the objective of this work is to analyze the interlaminar stresses in laminated hybrid composite cylindrical shell which is subjected to centrifugal body force using layerwise theory of Reddy (LWT). The model is under centrifugal forces caused by rotation of the cylinder about its axis. The principle of minimum total potential energy is used to obtain the governing equations of the rotating cylinder. The layerwise theory (LWT) of Reddy is employed for discretization of the governing equations to a system of ordinary dierential equations in terms of the displacement of numerical surfaces. To solve the equations of motion of the cylinder in the LWT, the equation is written in the decoupled form by de nition of modal space variables. An analytical solution is presented for governing equation. The solution is completed by imposing the boundary conditions in the edges of the cylinder. The interlaminar and in-plane stresses are obtained using the displacement eld of layerwise theory for the free and clamped boundary conditions. The interlaminar stresses in the Hybrid cylindrical shell are obtained using two dierent methods, the constitutive law of the numerical layers, and integrating the equilibrium equations of motion. To validate the results, the results of LWT for cross-ply cylindrical shell are compared to those of Finite element solution in the commercial nite element code Ansys. The results showed an excellent accuracy of the layerwise theory in calculating the interlaminar and in-plane stresses in hybrid cylinder. Various gures from the distribution of the stresses along the interfaces of layers and through the thickness of rotating cylinder are presented in the numerical results. The eects of the geometry, the types of layering, the speed of rotation and hybridation of laminated cylindrical shell on the interlaminar stresses are analyzed. Consequently, the delamination of the layered can be predicted and prevented.

Primer on dentin bonding groups contains hydrophilic groups so that it reacts on moist dentin surface and provides hybrid layer but since the enamel is hydrophobic tissue, this question will be raised that whether the use of dentin bonding to the enamel and dentin should be similar and with relative humidity Or when using the dentin bonding, enamel should be completely dry? The aim of this study was determine the amount of microleakage of single bond to dry and moist enamel in premolar teeth.
In this study 40 extracted premolars were selected and evaluated. A standard V-shaped groove in the buccal and lingual tooth was prepared. The samples were divided into two groups randomly. 37% phosphoric acid etchant was applied to the enamel surfaces in each group for 15 seconds and then rinsed with water for 20 seconds. In the first group, Enamel surface was completely dry, and the second group, the enamel surface remained wet. In both group Single bond of bonding agent was used. The specimens were subjected to thermocycling for 500 cycles. Then teeth were sectioned and microleakage of restorations was determined.
Microleakage of total-etch technique using single bond on wet enamel surface was significantly less than dry enamel surface (P = 0.033).
According to the statistical analysis should be before use of single bond, the complete drying enamel avoided, but excessive moisture is removed with a cotton pellet.

Tooth colored restorations are so common nowadays due to increased esthetic needs. A successful composite restoration demands a strong bonding with lowest microleakage. Close relation between tooth surface and the other adherents is an important factor in bond strength. The purpose of this study is to evaluate the effect of enamel moisture on tensile bond strength of composite resins using Single bond in total etch technique.

In this in vitro study, 40 premolar teeth were randomly divided into two equal groups. Enamel surface of the teeth were polished using a disk in midbuccal portion. The roots were dissected from 2mm below CEJ and midbuccal portion of the teeth were etched. In one group after rinsing the etchant, tooth surface was dried completely (group I). In the other group the surface moisture was removed using cotton pellet (group II). Single Bond (3M) was applied on desired surfaces and cured. Composite resin was layered over the tooth surface to 4mm height. The teeth were then mounted in the way that they can be placed in the holding device from lingual side. After that the teeth were placed in UTM device under tensile stress with the rate of 0.5 mm/min. the failure surface was examined to detect type and location of the failure. The data were analyzed using T-Test and Fisher's Exact test.

Data showed that although mean bond strength in group I was higher but the difference was not statistically significant. Type of failure in two groups was not statistically significant either.

Considering that there is no significant difference between the two groups and a little moisture is needed for creation of hybrid layer and bonding to dentine, leaving a bit moisture on enamel equal to that of dentine does not interfere with bonding to enamel and produce a good bond strength.

In some cases, deep caries incidence or trauma causes primary first deciduous teeth to loss prematurely which develops different complications such as space loss leading in delayed or urged eruption of permanent successors in turn. The objective of this study was to assess the effects of premature loss of primary first molars on 4-8 years old children referring to the Faculty of Dentistry of Qazvin University between the years 1387-1389. In this descriptive trial, 114 children (48 males, 66 females) subjected to the premature extraction of the primary first deciduous teeth were selected and underwent exact clinical examinations. The results were recorded in a questionnaire and the frequency and percent of different complications following premature loss of the primary first deciduous teeth were reported. In children with the premature loss of the primary first deciduous teeth, the mean space of canine distal and primary second molar mesial aspects was 6.34±1.96 mm in the extraction side and 8.28±0.82 in the control side. In 44 (38.6%) of the subjects, the primary second molar teeth drifted mesially and in 34 (29.8%) ones, the canine moved distally. In 36 (31.6%) individuals; the extracted teeth quickened the eruption of the permanent first premolars. The mean time passed from the teeth extractions was also 21.62 months. 25(21.9%) of subjects used space maintainers while the maintainer type was band and loop in the most cases (80%) and lingual arch in 20% of them. 28 (24.6%) individuals showed occlusal movement of the teeth in the opposite side of the extracted teeth and in 10 (8.8%) of cases, the permanent first premolar was rotated. 22 (19.3%) of cases showed spacing and 42 (36.8%) of them had crowding traits.Due to the different complications associated with the premature loss of the primary deciduous first molars, the development of suitable treatment and preventive cares will help children to achieve acceptable level of oral and dental health.