Stability Region of a Slotted Aloha Network with K-Exponential Backoff

Stability region of random access wireless networks is known for only simple network scenarios. The main problem in this respect is due to interaction among queues. When transmission probabilities during successive transmissions change, e.g., when exponential backoff mechanism is exploited, the interactions in the network are stimulated. In this paper, we derive the stability region of a buffered slotted Aloha network with K-exponential backoff mechanism, approximately, when a finite number of nodes exist. To this end, we propose a new approach in modeling the interaction among wireless nodes. In this approach, we model the network with inter-related quasi-birth-death (QBD) processes such that at each QBD corresponding to each node, a finite number of phases consider the status of the other nodes. Then, by exploiting the available theorems on stability of QBDs, we find the stability region. We show that exponential backoff mechanism is able to increase the area of the stability region of a simple slotted Aloha network with two nodes, more than 40\%. We also show that a slotted Aloha network with exponential backoff may perform very near to ideal scheduling. The accuracy of our modeling approach is verified by simulation in different conditions.Comment: 30 pages, 6 figure

Analysis of Network Coding in a Slotted ALOHA-based Two-Way Relay Network

This paper deals with a two-way relay network (TWRN) based on a slotted ALOHA protocol which utilizes network coding to exchange the packets. We proposed an analytical approach to study the behavior of such networks and the effects of network coding on the throughput, power, and queueing delay of the relay node. In addition, when end nodes are not saturated, our approach enables us to achieve the stability region of the network in different situations. Finally, we carry out some simulation to confirm the validity of the proposed analytical approach

Selecting drill size for post space preparation based on final endodontic radiographs: An in vitro study

BACKGROUND: For placement of intraradicular posts the intracanal filling material has to be removed. If drills are employed for this purpose, extra widening of the canal, incomplete cracks or root perforation are probable when inappropriate size of drill is used. OBJECTIVE: This in vitro study assessed the efficacy of radiographs taken after completion of root canal therapy in selecting the appropriate-sized Peeso reamer for post space preparation. METHODS: Canals of 53 extracted maxillary and mandibular teeth of different types were cleaned and shaped. Then with acrylic resin 3-dimensional model of the intracanal space of each tooth was fabricated. Next, all canals were filled with gutta-percha and teeth were radiographed buccolingually. Based on these radiographs two observers selected a Peeso reamer that best matched each canal’s diameter. The diameter of the selected Peeso reamer was compared to the diameter of the corresponding resin model of each canal by two independent observers and the difference was measured. The data were analyzed by paired sample t-test using SPSS version 22. RESULTS: The diameter of the selected Peeso reamers ranged from 0.21 mm smaller to 0.12 mm larger than the diameter of intracanal spaces. The difference between reamer and resin model was less than 0.1 mm in 75% of the cases. CONCLUSION: The result of this study suggests that post-operation endodontic radiographs are reliable means for selecting a size of Peeso reamer that does not encroach on dentinal wall during removal of intracanal filling material and post space preparation

The Effect of BC Sealer, AH-Plus and Dorifill on Push-out Bond Strength of Fiber Post

Introduction: Dentinal canal walls are in direct contact with endodontic sealers prior to post space preparation and luting cements after post space preparation. This direct contact may affect the bond strength of intraradicular posts to root dentin. This study aimed to assess the effect of three different sealers on the bond strength of fiber posts to root dentin. Methods and Materials: The canals of 56 extracted single-rooted human premolars after selection and decoronation were prepared. For obturation of the canals, specimens were randomly divided into four groups (n=14) according to the type of sealer used in conjunction with gutta-percha: group 1 (control) without any sealer; group 2 with AH-Plus sealer (resin based); group 3 with Dorifill sealer (ZOE-based); and group 4 with BC Sealer (calcium silicate-based). Nine mm-deep post space was prepared in the canal of each specimen. Intraradicular fiber posts were cemented using dual-cure resin cement (Panavia F2.0). Sections of 1 mm thickness were made at the coronal, middle and apical thirds of the post space of each specimen. The push-out bond strength of post to root dentin was measured in a universal testing machine. The data were analyzed using one-way ANOVA and post-hoc Tukey’s test. Results: The mean push-out bond strength in the coronal third was significantly lower in Dorifill group compared to AH-Plus (P=0.004). This value was significantly lower in BC Sealer group than AH-Plus (P=0.000) and control group (P=0.03). In middle and apical thirds, the mean push-out bond strength was not significantly different among the four groups (P=0.407, P=0.065, respectively). The mean push-out bond strength was significantly lower in apical than coronal third in AH-Plus group (P=0.001). Conclusion: Application of BC Sealer and Dorifill decreased the mean push-out bond strength of intracanal post to root dentin in the coronal third in comparison to AH-Plus.Keywords: Bond Strength; Endodontic Sealer; Fiber Post; Resin Cemen

Effect of cement type and thickness on push-out bond strength of fiber posts

Background. This study investigated the effect of the thickness of two resin cements on push-out bond strength of fiber posts to root dentin. Methods. Sixty decoronated single-rooted teeth were endodontically treated. The specimens were then randomly allocated to two groups (n=30); group 1: drill size 90 w, matching the size of fiber posts used; group 2: drill size 110, larger than the posts. The specimens in each group were divided into 2 subgroups (n=15); subgroup SE, in which the posts were cemented with self-etch Panavia F2.0 and subgroup SA, in which self-adhesive Panavia cement was used. After 72 hours, 2 slices with 1 mm of thickness were prepared from the mid-root of each specimen. Push-out bond strength test was performed in a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed with two-way ANOVA and t-test. Results. The mean bond strengths of the posts cemented in matched-size spaces for SE and SA groups were 4.02±1.6 and 4.12±2.3 MPa, respectively. For posts cemented in oversized spaces, the values were 4.9±2.3 and 2.8±1.3 MPa, respectively. In matched-size spaces, there was no significant difference between the two groups. Conclusion. The results of this study suggested that increasing the cement thickness would reduce the bond strength of fiber posts to root dentin when self-adhesive cements are used; however, self-etch adhesives were not affected

Effect of Die Materials on Marginal and Internal Adaptation of Zirconia Copings: An In Vitro Study

Aim: Close adaptation of cemented CAD/CAM restorations to their abutments is highly dependent on precise impressions and accurate replicas of teeth and adjacent oral tissues. This in-vitro study compared the effect of two die materials, as physical replicas of prepared teeth, on internal and marginal adaptations of zirconia copings to their corresponding abutments. Materials and Methods: A virtual model simulating a prepared premolar was designed and used for the milling of thirty identical metal models. Impression was taken of all models by Polyvinyl siloxane material. Fifteen impressions were poured in with Type IV stone and the other fifteen with polyurethane resin to make dies. All dies were scanned, and for each of them, zirconia coping was designed and milled. The copings were cemented to their corresponding metal models. Marginal gap between each coping and its metal model was measured at 20 points with a stereomicroscope (×60). Then the specimens were sectioned into two halves, and the internal gap was measured at seven points, including right and left cervico-axial, mid-axial, occluso-axial, and mid-occlusal. The data were analyzed with an independent T-test and repeated measure ANOVA at a 95% confidence level (p<0.05). Results: Mean value of marginal gap for Type IV stone and Exakto-Form groups were 54.31 ± 4.11 μm and 56.25 ± 4.24 μm, respectively. Mean values of the internal gaps for both groups ranged from 48 μm to 120 μm. Conclusion: Based on the results of this study, an internal and marginal adaptation of zirconia copings designed on digitized polyurethane and Type IV stone dies are clinically acceptable

The Effects of Sex Hormones on Liver Regeneration after Liver Trauma in Animal Model

Background: The surgical management of liver injuries remains a great challenge for the traumatologists and general surgeons. We hypothesized that administration of 17 â-estradiol, a female sex hormone, improves&nbsp;hepatocellular healing after liver trauma.Methods: In an experimental model, 60 rats were divided into six subgroups: A (male control), B (male and estradiol), C (castrated male and estradiol), D (female control), F (female and estradiol), and G&nbsp;(oopherectomized female). After inducing liver trauma, estradiol subgroups received 3 doses of intravenous 17 â-estradiol (1 mg/kg) every 8 hours. 2 weeks post trauma, animals were sacrificed and hepatocellular regeneration was measured with the help of stereologic parameters of regeneration. Hepatocellular healing was compared between previous left lobe samples and the new post-traumatic right lobe samples.Results: Stereological parameters of rats receiving 17 b-estradiol after trauma was much better regarding mean angiogenesis point counting and volume density, compared with non-receiver groups after 2 weeks of trauma (P &lt; 0.005). There was no significant difference for hepatocyte nucleus, hepatocyte point counting and volume density between estradiol receiver and non-receiver groups. In a comparison between subgroups, female sex had the same effect as giving estradiol. Oopherectomized female rats had more fibrogenesis but less angiogenesis (P &lt; 0.005). Fibrogenesis was more in groups that were estradiol non-receiver (P &lt; 0.005). In an explicit comparison of control females and males, estradiol infused males and females, and castrated male or oopherectomized female groups showed that stereological parameters of hepatocyte and hepatocyte nucleus were lower in female subgroups, but angiogenesis was better for female groups except for oopherectomized females.Conclusions: This study did support the administration of exogenic female hormone as an approach to augment the angiogenesis as a good index of regeneration for traumatic liver in rats

Application of Outlier Robust Nonlinear Mixed Effect Estimation in Examining the Effect of Phenylephrine in Rat Corpus Cavernosum

Abstract Ignoring two main characteristics of the concentration-response data, correlation between observations and presence of outliers, may lead to misleading results. Therefore, the special method should be considered. The present study was designed to apply the outlier robust nonlinear mixed estimation for effects of phenylephrine on rat corpus cavernosum strips. In this study, eight different doses of phenylephrine in eight experimental groups were used. Each group consisted of eight rats. The concentration-response curves to phenylephrine (0.1µM to 300µM) were obtained by the cumulative addition of phenylephrine to the chamber. Because of the existence of an outlier to achieve robust estimations, M-estimation method and Huber function as a dispersion function were used. Cumulative administration of phenylephrine (0.1µM -300µM) caused concentration-dependent contractions in strips of rat corpus cavernosum (-Log EC 50 was 5 ± 0.31, 95% CI= 5.92 to 4.21). The contraction of corpus cavernosum started in the concentration of 0.3 μM and then gradually increased in a dose-dependent manner till it reached a plateau in 100 μM. To consider the clustering feature of concentration-response data, the 4pl regression with a random term has been used. To estimate parameters, because of existence of an outlier in dataset, the robust procedure has been applied. The contraction of corpus cavernosum started in the concentration of 0.3 μM and then gradually increased in a dose-dependent manner till it reached a plateau in 100 μM

Prosthodontic using Rapid Prototyping

Rapid prototyping is a set of technicality which applied to create a scale model of a physical part or assembly rapidly utilizing three-dimensional computer aided design (CAD) data. 3D printing or "additive layer manufacturing" technology was used to Develop the part or assembly. It is a CAD/CAM technology which was created initially to manufacture prototypes for industrial purposes. RP technology   encouraged the configuration and quick generation of mass quantities of precise parts by the industrial  manufacturing in a convenient time with exactness and pace. In the previous two decades this technology was utilized  efficiently in the medical field with a promising results. In this review the technique, methods and various uses of this fast emerging technology regarding prosthodontic will be discussed

The Effect of 1% Pilocarpine Mouthwash on Salivary Flow Rate in Patients with Radiation-Induced Xerostomia: A Double-Blind Randomized Clinical Trial

Background: Radiation-induced hyposalivation is a common complication of radiotherapy for head and neck cancers. The most commonly prescribed medication for hyposalivation is pilocarpine. However, due to the numerous systemic side-effects associated with pilocarpine, there has been a proposal to use it as a mouthwash. This study aimed to evaluate the impact of 1% pilocarpine mouthwash on salivary flow in patients with radiation-induced xerostomia.Method: This double-blind, randomized clinical trial involved 63 patients with radiation-induced xerostomia. The patients were randomly allocated into the pilocarpine hydrochloride 1% mouthwash group and the placebo one. Patients were instructed to use these mouthwashes four times a day, with 30 drops each time, for two minutes. Unstimulated saliva production in patients was measured using the spitting method at three stages: two weeks before the commencement of radiotherapy, two weeks after, and four weeks after the completion of radiotherapy. These measurements were then compared between the two groups. Statistical analysis included chi-square, independent t-test, and Analysis of Variance (ANOVA) with repeated measures and the Sidak post hoc test. Statistical analysis was conducted using SPSS 17, and a significance level of P < 0.05 was applied.Results: A comparison of saliva secretion between the pilocarpine mouthwash group and the control group at various time points after radiotherapy revealed that saliva secretion in the control group significantly decreased compared with the pilocarpine mouthwash group (P < 0.001).Conclusion: 1% pilocarpine mouthwash is recommended for managing radiationinduced xerostomia