148 research outputs found
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
Cardiovascular risk factors in young male adults: impact of physical activity and parental education
Background: This study was conducted to assess whether choices of physical activity, smoking status, and parental education and income were correlated with the health status of young adult males which are important for preventive health policy. Methods: 491 18-29-year old males from lower socioeconomical districts in Turkey participated in this study. Information about demographic characteristics, parental education, household income, smoking status, and physical activity was obtained by means of a standardized questionnaire. BMI and metabolic parameters (serum lipid profile) were assessed.Results: Mean total cholesterol, LDL, HDL and triglyceride levels were in the normal range. The physically active group displayed a better lipid profile. No relationship was found between parental education and serum lipids. Smoking was slightly correlated with household income (r=103, p=0.022).Conclusion: Young adult males who participate in relatively high levels of physical activity are at lower CHD risk than less active ones. The present study also showed that lower socioecnomic status does not always correlate with higher levels of cardiovascular risk factors. In conclusion, data supports that while family history cannot be changed, HDL levels can be modulated by lifestyle factors as in other populations and that with the determined benefits of increasing physical activity and thus, HDL levels, policy reform in schools to promote physical activity are warranted
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 (
Association between Admission Mean Platelet Volume and ST Segment Resolution after Thrombolytic Therapy for Acute Myocardial Infarction
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
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