Performance analysis of the carrier-sense multiple access protocol for future generation wireless networks

Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Science of Bilkent University, 2013.Thesis (Ph. D.) -- Bilkent University, 2013.Includes bibliographical references leaves 115-127.Variants of the carrier-sense multiple access (CSMA) protocol has been employed in many communications protocols such as the IEEE 802.11 and Ethernet standards. CSMA based medium access control (MAC) mechanisms have been recently proposed for other communications scenarios such as sensor networks and acoustical underwater networks. Despite its widespread use, the performance of the CSMA protocol is not well-studied from the perspective of these newly encountered networking scenarios. We here investigate the performance of the CSMA protocol from the point of three different aspects: throughput in networks with large propagation delay, short-term fairness for delay sensitive applications in large networks and energy efficiency-throughput trade-off in networks with battery operated devices. Firstly, we investigate the performance of the CSMA protocol for channels with large propagation delay. Such channels are recently encountered in underwater acoustic networks and in terrestrial wireless networks covering larger areas. However, a mathematical model of CSMA performance in such networks is not known. We propose a semi-Markov model for a 2-node CSMA channel and then extend this model for arbitrary number of users. Using this model, we obtain the optimum symmetric probing rate that achieves the maximum network throughput as a function of the average propagation delay, ¯d, and the number of nodes sharing the channel, N. The proposed model predicts that the total capacity decreases with ¯d −1 as N goes to infinity when all nodes probe the channel at the optimum rate. The optimum probing rate for each node decreases with 1/N and the total optimum probing rate decreases faster than ¯d −1 as N goes to infinity. Secondly, we investigate whether the short-term fairness of a large CSMA network degrades with the network size and density. Our results suggest that (a) the throughput region that can be achieved within the acceptable limits of shortterm fairness reduces as the number of contending neighboring nodes increases for random regular conflict graphs, (b) short-term fair capacity weakly depends on the network size for a random regular conflict graph but a stronger dependence is observed for a grid topology. We also present related results from the statistical physics literature on long-range correlations in large systems and point out the relation between these results and short-term fairness of CSMA systems. Thirdly, we investigate the energy efficiency of a CSMA network proposing a model for the energy consumption of a node as a function of its throughput. We show that operating the CSMA network at a very high or at a very low throughput is energy inefficient because of increasing carrier-sensing and sleeping costs, respectively. Achieving a balance between these two opposite operating regimes, we derive the energy-optimum carrier-sensing rate and the energy-optimum throughput which maximize the number of transmitted bits for a given energy budget. For the single-hop case, we show that the energy-optimum total throughput increases as the number of nodes sharing the channel increases. For the multi-hop case, we show that the energy-optimum throughput decreases as the degree of the conflict graph of the network increases. For both cases, the energy-optimum throughput reduces as the power required for carrier-sensing increases. The energy-optimum throughput is also shown to be substantially lower than the maximum throughput and the gap increases as the degree of the conflict graph increases for multi-hop networks.Köseoğlu, MehmetPh.D

Joint path and resource selection for OBS grids with adaptive offset based QOS mechanism

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2007.Thesis (Master's) -- Bilkent University, 2007.Includes bibliographical references leaves 71-76It is predicted that grid computing will be available for consumers performing their daily computational needs with the deployment of high bandwidth optical networks. Optical burst switching is a suitable switching technology for this kind of consumer grid networks because of its bandwidth granularity. However, high loss rates inherent in OBS has to be addressed to establish a reliable transmission infrastructure. In this thesis, we propose mechanisms to reduce loss rates in an OBS grid scenario by using network-aware resource selection and adaptive offset determination. We first propose a congestion-based joint resource and path selection algorithm. We show that path switching and network-aware resource selection can reduce burst loss probability and average completion time of grid jobs compared to the algorithms that are separately selecting paths and grid resources. In addition to joint resource and path selection, we present an adaptive offset algorithm for grid bursts which minimizes the average completion time. We show that the adaptive offset based QoS mechanism significantly reduces the job completion times by exploiting the trade-off between decreasing loss probability and increasing delay as a result of the extra offset time.Köseoğlu, MehmetM.S

Detection of preanalytical errors in arterial blood gas analysis

Blood gas analysis (BGA) is an essential test used for years to provide vital information in critically ill patients. However, the instability of the blood gases is a problem. We aimed to evaluate time and temperature effects on blood gas stability. Arterial blood was collected from 20 patients into syringes. Following BGA for baseline, syringes were divided into groups to stand at 4°C and 22°C for 30, 60, 90, 120 minutes. All were tested for pH, partial pressure of carbon dioxide (pCO2), partial pressure of oxygen (pO2), oxygen saturation (sO2), oxyhemoglobin (O2Hb), sodium, potassium, glucose, lactate, oxygen tension at 50% hemoglobin saturation (p50), and bicarbonate. A subgroup analysis was performed to detect the effect of air on results during storage. Percentage deviations were calculated and compared against the preset quality specifications for allowable total error. At 4°C, pO2 was the least stable parameter. At 22°C, pO2 remained stable for 120 min, pH and glucose for 90 min, lactate and pCO2 for 60 min. Glucose and lactate were stable when chilled. Air bubbles interfered pO2 regardless of temperatures, whereas pCO2 increased significantly at 22°C after 30 min, and pH decreased after 90 min. Bicarbonate, sO2, O2Hb, sodium, and potassium were the unaffected parameters. Correct BGA results are essential, and arterial sample is precious. Therefore, if immediate analysis cannot be performed, up to one hour, syringes stored at room temperature will give reliable results when care is taken to minimize air within the blood gas specimen

Evaluation of YouTube Videos Quality of Pediatric Cardiac Surgery Anesthesia

Introduction:To evaluate the quality of YouTube videos on pediatric cardiac surgery anesthesia (PCSA).Methods:The keywords including, “PCSA”, “pediatric cardiac surgery”, and “pediatric anesthesia” were browsed on YouTube between January 1st, 2023 and January 10th, 2023. Video characteristics were recorded. The modified DISCERN instrument, the Global Quality Score (GQS), and the Patient Education Materials Assessment Tool (PEMAT) were used to evaluate the quality of the videos. The videos were divided into two groups as professionals (doctor, nurse, hospital, etc.) and non-professional (patient, non-health institutions, etc.) according to the upload source.Results:A total 82 of the videos were included in the study. Fifty-six (68.3%) videos were uploaded by professional sources and 26 (31.7%) were by non-professional sources. Statistically, the average like of the videos uploaded by professional sources were significantly higher (64.0 and 29.0, p=0.005). The average number of comments on professionally sourced videos was 46.0, and it was 30.0 for non-professional videos (p=0.015). The GQS was 3.7±1.0 for professional videos and 2.2±0.8 for non-professional videos (p=0.001). The Modified DISCERN score was found to be significantly higher in the professional videos (p=0.001). The PEMAT score was above 70% in 50 (89.3%) videos in the professional video group and 12 (46.1%) videos in the non-professional video group (p=0.001).Conclusion:Our findings revealed that professional videos about PCSA had significantly higher “likes” number and comments rate and YouTube videos about PCSA, which were shared by professional healthcare providers had significantly higher modified DISCERN score, GQS, and PEMAT score

KARE VE ÜÇGEN DİZİLİŞLİ NOZUL SİSTEMLERİ KULLANILARAK GERÇEKLEŞTİRİLEN CAM TEMPERLEME İŞLEMİNDE PARÇACIK SAYININ NUSSELT SAYISINA BAĞLI OLARAK DEĞİŞİMİ

Camın temper kalitesini etkileyen en önemli parametreler ısıtma ve ani soğutma süreleridir. Isıtma süresini; camın kimyasal bileşimi, kütlesi, ulaşacağı yüzey ortalama sıcaklığı, fırının gücü gibi parametreler etkilerken, ani soğutma süresini ise camın ani soğutma ünitesinin önüne geldiği andaki yüzey sıcaklığı, soğutma sonu yüzey sıcaklığı, soğutma ünitesinin konfigürasyonu (nozul-plaka arası mesafenin nozul çapına oranı H/D, nozul-nozul arası mesafenin nozul çapına oranı S/D, nozul dizilişi) ve Reynolds sayısı etkilemektedir. Bu çalışmada; 4 mm kalınlığındaki düz camın temperleme sürecinde kare ve üçgen dizilişli nozul sistemleri kullanılarak (S/D=2) ani soğutulması ve bu süreçte ortalama Nusselt sayısının parçacık sayısına etkisi incelenmiştir. Çalışma Re=15000, 17500, 20000, 22500 ve 25000 değerlerinde, H/D=2, 4, 6, 8 ve 10 oranlarında gerçekleştirilmiştir. Çalışma sonunda, parçacık sayısının ortalama Nusselt sayısı ile doğru orantılı olarak değiştiği saptanmıştır. S/D=2 oranı için en uygun soğutma şartları; üçgen diziliş, Re=15000 değerinde ve 2≤H/D≤4 oranında elde edilmiştir

Effect of sumac extract on serum oxidative status, RANKL/OPG system and alveolar bone loss in experimental periodontitis in rats

Objectives Sumac (Rhus coriaria L.) is widely used spice which has several properties such as antioxidant, anti-inflammatory and antimicrobial. The purpose of this animal study was to evaluate the effects of sumac extract on levels of receptor activator of nuclear factor-kappa B ligand (RANKL), osteoprotegerin (OPG) expression, serum oxidative status, and alveolar bone loss in experimental periodontitis. Material and Methods Twenty-four Wistar rats were separated into three groups: non-ligated (NL, n=8), ligature only (LO, n=8), and ligature and treated with sumac extract (S, n=8) (20 mg/kg per day for 11 days). A 4/0 silk suture was placed around the mandibular right first molars subgingivally; after 11 days, the rats were sacrificed, and alveolar bone loss was histometrically measured. The detection of RANKL and OPG were immunohistochemically performed. Levels of serum total antioxidant status (TAS)/total oxidant status (TOS), and oxidative stress index (OSI) were also analyzed. Results Alveolar bone loss was significantly greater in the LO group compared to the S and NL groups (

Maksiller yan keser dişteki aksesuar kök nedeniyle oluşan periodontal cebin tedavisi: Olgu sunumu

Servikal mine uzantıları, mine incileri ve palatal yivler gibi diş ile ilişkili faktörler periodontal hastalık oluşumuna neden olabilirler. Aksesuar kök oluşumu nadir görülen anomalilerdendir. Bu rapor kronik periodontitisli 63 yaşındaki erkek hastanın vaka sunumudur. Maksiller sol yan keser dişin kökünün mesio-palatinal yüzeyinde 7 mm cep derinliği ile birlikte aksesuar kök benzeri yapı tanımlanmıştır. Bu aksesuar kök benzeri yapı faz I periodontal tedavi ve endodontik tedavi sonrası cerrahi olarak eksize edilmiştir. Cerrahi sonrası periodontal iyileşme sorunsuzdu ve periodontal cep derinliği cerrahiden 3 ay sonra 7mm’den 4mm’ye düşmüştür. Bu dental anomalilerin erken tespiti, periodontitisin etkin tedavisinde büyük klinik öneme sahipti

Assesment of flow volume and anastomosis diameter in native arteriovenous fistulas using doppler ultrasound

Nativ hemodiyaliz arteriyovenöz fistüllü (AVF) hastalarda brakiyal arter akım volümü ile AVF anastomoz çapı arasındaki ilişkiyi araştırmak. Toplam 16 nativ AVF'li hasta değerlendirildi.16 hastanın 11'inde AVF üst kolda (brakiyobazilik ya da brakiyosefalik) 5'inde ise ön kolda (radiyosefalik) yer almaktaydı. OrtalamaAVF süresi 24 aydı.16 hastanın 12'si semptomsuzdu. 4 hastada ise üst ekstremitede ödem mevcuttu. Doppler ultrasonografi ile AVF' lerde brakiyal arter akım volümü ve AVF anastomoz genişliği ölçüldü. Üst ekstremitede ödem bulunan 4 hastanın 3'üne fistülografi yapılarak ödem etiyolojisi araştırıldı. 16 hastanın 14'ünde brakiyal arter volümü 2000ml/dk altında ölçüldü. Bu hastalardaAVF anastomoz genişliği ortalama 3.6 mm idi. Brakiyal arter akım volümü 2000ml/dk üzerinde ölçülen 2 hastada (4400ml/dk, 6000ml/dk) AVF anastomoz genişliği sırasıyla 6.9mm ve 10mm idi. Fistülografi yapılan 3 hastanın 2'sinde sunklavyan vende tromboz, 1'inde darlık saptandı. Doppler ultrasonografi ile AVF'lerde akım volümü hesaplanabilir. Bizim çalışmamızda, yüksek akım volümüne sahipAVF'lerde anastomoz genişliği normal volümlü hastalara göre daha fazla idi. Artmış anastomoz genişliği yüksek akım volümünün sebebi olabilir.The aim of this study was to evaluate flow volume and anastomosis diameter of native arteriovenous fistulas(AVF). 16 patients with native AVF were evaluated using Doppler Ultrasound. Eleven of 16 patients had upper arm AVF (bachiocephalic or brachiobasillic) and 5 of 16 patinets had forearm AVF (radiocephalic). Twelve of 16 patients had not symptoms. There was edema of upper extremity in 4 patients.Brachial artery flow volume andAVF anastomosis diameter were calculated using Doppler ultrasound. Fistulography was performed on 3 of the 4 patients who had upper extremity edema. The brachial artery flow volume was calculated to be less than 2000ml/min in 14 of the 16 patients. The mean AVF anastomosis diameter was 3.6 mm in these patients. Whose flow volume of brachial artery were 4400ml/min and 6000ml/min. The diameters of AVF anastomosis were 6.9 mm and 10 mm in the 2 patients. Whose fistulography showed subclavian vein thrombosis in 2 patients and subclavian vein stenosis in 1 patient. In this study, diameter ofAVF anastomosis with high flow volume was greater than diameter ofAVF anastomosis with normal flow volume. Increased diameter of AVF anastomosis may be responsible for an increased flow volume ofAVF