Extensive researches on Wireless Sensor Networks (WSNs) have been performed and many techniques have been developed for the data link (MAC) layer. Most of them assume single-CHANNEL MAC protocols. In the usual dense deployment of the sensor networks, single-CHANNEL MAC protocols may be deficient because of radio collisions and limited bandwidth. Hence, using multiple CHANNELs can significantly improve the performance of WSN. Recent developments in sensor technology, as seen in Crossbow’s MICAz Mote, Rockwell’s WINS nodes and IEEE 802.15.4 Zigbee, have enabled support for multi-CHANNEL communications. Several multi-CHANNEL MAC protocols with different objectives have been proposed for WSNs in literature. This paper surveys and classifies the state-of-the-art multiCHANNEL MAC protocols that are proposed for WSNs. It first outlines the sensor network properties that are crucial for designing a MAC protocol. It subsequently reviews the existent challenges to design a good multi-CHANNEL MAC protocol for the sensor networks. Then, several multi-CHANNEL MAC protocols specifically proposed for the WSNs are inspected in detail and compared with each other. Finally, some open issues in this area are outlined for future research.

In this paper, we aim to study a 𝒍-user quantum multiple ACCESS wiretap CHANNEL with an arbitrary number of wiretappers under one-shot setting. In this regard, we first introduce the general quantum multiple ACCESS wiretap CHANNEL and the simplified proposed CHANNEL. Then, we calculate an achievable secrecy rate region for the main CHANNEL with two users. The encoding process uses the superposition and wiretap coding techniques, and the decoding technique is based on the simultaneous decoder. Also, Convex splitting is used to satisfy security requirements. At last, we extend the results to the l-user case.

In this study, we introduce a new two-way relay CHANNEL and obtain an inner bound and an outer bound for the discrete and memoryless multiple ACCESS relay CHANNELs with receiver-source feedback via two-way relay CHANNEL in which end nodes exchange signals by a relay node. And we extend these results to the Gaussian case. By numerical computing, we show that our inner bound is the same with one obtained by Hou-Koetter-Kramer, for the CHANNEL with relay-source feedback.

Introduction: A limited number of studies have evaluated factors influencing the retention of fixed prostheses cemented to implant abutments. The aim of this study was to compare the effect of varying degrees of screw ACCESS CHANNEL obturation on retention of implant-supported cast fixed restorations.Materials& Methods: In this experimental study, 40 implant abutments with a diameter of 4.5 mm were connected to implant analogues and mounted in acrylic resin blocks. The samples were divided into four groups randomly. In groups 1, 2 and 3, the ACCESS CHANNELs were obturated with a 1-mm, 2-mm and 3-mm free space and in group 4 the ACCESS CHANNELs were obturated completely with silicone material and the copings were cemented with a temporary bonding agent containing eugenol. After thermocycling, the retention of the samples was evaluated in a universal testing machine under 5000 N at a strain rate of 5 mm/min. Data were analyzed with oneway ANOVA and post hoc LSD test (a=0.05).Results: The mean retention for the group with abutment ACCESS CHANNEL completely obturated was less than that in others. One-way ANOVA showed statistically significant differences between the groups (p value=0.032). The difference between the group with completely obturated ACCESS CHANNELs and the other groups was significant (p value<0.05); however, the differences between the groups obturated with 1-mm, 2-mm and 3-mm free spaces were not statistically significant (p value>0.05).Conclusion: The retention of castings cemented to implant abutments might be influenced by the obturation mode of screw ACCESS CHANNEL. Complete obturation of ACCESS CHANNEL with poly vinyl siloxane results in a decrease in retention.

Introduction: There is limited data on the factors affecting the retention of cemented fixed prostheses to implant abutment. The aim of this study was to evaluate the effect of screw ACCESS CHANNEL filling method and cement type on retention of implant-supported fixed restorations.Materials and Methods: In this experimental study, 40 implant analogs were mounted in autopolymerizing acrylic resin blocks, and two-piece titanium abutments were placed in each implant analog. Twenty abutment samples were completely filled with silicone, and 20 other samples were filled partially. In each of the study groups, Temp BondÒ eugenol-containing temporary cement was used for 10 samples, while in another 10 samples non-eugenol temporary cements were utilized. Prior to the retention test, samples were placed in the rmocycling machine with 1000 cycles for 24 h. Each sample was stretched using a Universal Pull-out Test Machine with a force of 5000 N. The required load for removing the crown was recorded. The data was analyzed USING two-way ANOVA and least square difference (a=0.05).Results: Among the four groups, the highest retention rate was observed in the group of partial screw ACCESS CHANNEL filling with eugenol cement. Also, the rate of retention in the group of complete screw ACCESS CHANNEL filling with non-eugenol cement was significantly lower than in any other group. A significant difference was observed between all the groups except for the groups of complete screw ACCESS CHANNEL filling with eugenol cement and partial screw ACCESS CHANNEL filling with non-eugenol cement (P=0.27).Conclusion: The mean rate of retention in partial ACCESS cavity filling group was greater than that of the complete ACCESS cavity filling group; moreover, this rate was higher in the eugenol cement group than the non-eugenol cement group.

Background: AngioACCESS is one of the main treatment procedures for surgeons considering dialysis patients. End stage renal disease patients have to spend most of their lives under dialysis; therefore, given the high expenditure of angioACCESS surgeries, this study was conducted to evaluate the patency rate and complications of arteriovenous ACCESS operations.Methods: In this prospective study, 169 patients underwent 311 ACCESS surgeries for hemodialysis. Data was collected through questionnaires and analyzed by SPSS.Findings: Life table analysis showed that of 169 patients with fistulas, 84.9% of cases were patent after 2 months, and 80.5% and 73% were patent after 4 and 6 months, respectively. There was no significant difference between diabetic and non-diabetic patients patency rate in cubital ACCESS, but the patency rate in distal fistulas was significantly lower in diabetics. Different complications were recorded in 48.6% of patients, mainly heart failure and mild edema.Conclusion: Diabetes was higher among our cases than normal population which can be due to poor screening programs and low information on risks and correct follow-up of patients. In diabetic patients, cubital fistulas should be considered prior to distal ACCESSes. Complication rate in our study was higher than those reported. Since complications are significantly surgeon dependent, more attention to residential education and participating in related workshops can be helpful.

Introduction: One of the important factors in the success of implant-supported prostheses is the marginal fit of abutment-restorations. The aim of this study was to evaluate the effect of screw ACCESS CHANNEL filling method and cement type on the marginal adaptation of implant-supported fixed restorations. Introduction: One of the important factors in the success of implant-supported prostheses is the marginal fit of abutment-restorations. The aim of this study was to evaluate the effect of screw ACCESS CHANNEL filling method and cement type on the marginal adaptation of implant-supported fixed restorations. Materials and Methods: In this experimental in vitro study, 40 implant analogs were mounted in autopolymerizing acrylic resin blocks using a dental surveyor. Forty two piece titanium abutments were placed in each implant analog and torque up to 35 N cm. The following acrylic blocks of implants were randomly divided into 2 groups, including 20 abutment samples fully filled by the silicone, and 20 abutments sample filled partially with silicon. The marginal discrepancy of samples was measured from 4 sides with a magnification of ×50 by stereomicroscope before final cementation. In each study group, 10 samples were cemented by zinc-oxide eugenol temporary cement and 10 other samples with zinc-oxide non-eugenol temporary cement. The marginal discrepancy was measured at the same points again. Data were analyzed with ANOVA and, t-test (α =0. 05). Results: In all surfaces there were no significant differences in the mean marginal discrepancy between the group in which screw ACCESS CHANNELs were partially filled and the group in which screw ACCESS CHANNELs were completely filled before (P˃ 0. 05)and after (P=0. 052) cementation. However after cementation significant differences were found between the means of marginal discrepancy in two cement types (P=0. 02). Non-eugenol cement showed significantly higher marginal discrepancy than eugenol cement (P=0. 03). Conclusion: The mean marginal discrepancy in both full and partial ACCESS cavity filling groups did not differ significantly, but a marginal discrepancy with the use of non-eugenol cement was greater than eugenol cement.

Background: While considering the rise in the mean age of the chronic renal failure (CRF) patients and increasing frequency of those who need constant hemodialysis, the creation of a native arteriovenous fistula (AVF) is not possible, which could be due to the inACCESSibility of the superficial veins. This study was conducted to evaluate the efficacy of the vascular ACCESS, using cryopreserved jugular vein.Materials and Methods: In this experimental study, 15 sheep (Wt.= 30-40 kg) were selected between the year 2001 and 2002. The external jugular vein of each sheep was excised and after cryopreservation was put in liquid nitrogen (-196°C). Twenty-eight days later, the sample veins were used as allograft (in another sheep), and autograft (in the same sheep) and were placed between carotid artery and external jugular vein as bridge AVF. The efficacy, function, and patency were evaluated using doppler sonography and pathologic report.Results: Patency rate of sample was 100% after 3 months in both allografts and autografts. Thrombosis, hematoma, and infection were not seen. No inflammation was detected in pathologic report.Conclusion: This study showed that using allograft vein for vascular ACCESS is feasible and suitable, and it is recommended specially for those with previously infected fistula.