Fakülteler / Faculties
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Item The Capacitance/Conductance And Surface State Intensity Characteristics Of The Al/(Cmat)/P-Si Structures(Başkent Üniversitesi Fen Edebiyat Fakültesi, 2024-02-01) Cetinkaya, H. G.; Bengi, S.; Sevgili, O.; Altindal, S.To determine the Al/(CMAT)/p-Si structure's admittance analysis, capacitance/conductance versus frequency (C/G-V-f) data was obtained in the 3 kHz-3 MHz and -2/4 V ranges at room temperature. The powder form of CeMgAl11O19: Tb (CMAT) was thermally evaporated onto the front of p-Si wafer at 10-6 Torr as interfacial layer. From the Nicollian and Brews method, voltage-dependent spectra of Rs were derived for various frequencies. The parallel conductance and low-high frequency capacitance (CLF-CHF) techniques, respectively, were used to determine the voltage and frequency dependent spectra of Nss and their lifetime (tau). Surface states (Nss), which are identified by admittance measurements, emerge at the M/S interlayer because of high capacitance and conductance values at low frequencies. This can also be explained by the Nss's ability to track ac signals well at lower frequencies. The normalized parallel conductance versus frequency (Gp/omega-f) plot under various biases shows a peak because of Nss existence. x-ray diffractometer (XRD) was used for structural investigation and the average crystal size (D) of the nanocrystals (CMAT) was found to be less than 0.34 nm by using the Debye-Scherer's equation.Item The Capacitance/Conductance And Surface State Intensity Characteristics Of The Al/(CMAT)/p-Si Structures(PHYSICA SCRIPTA, 2024-01-24) Cetinkaya, H. G.; Bengi, S.; Sevgili, O.; Altindal, S.To determine the Al/(CMAT)/p-Si structure's admittance analysis, capacitance/conductance versus frequency (C/G-V-f) data was obtained in the 3 kHz-3 MHz and -2/4 V ranges at room temperature. The powder form of CeMgAl11O19: Tb (CMAT) was thermally evaporated onto the front of p-Si wafer at 10-6 Torr as interfacial layer. From the Nicollian and Brews method, voltage-dependent spectra of Rs were derived for various frequencies. The parallel conductance and low-high frequency capacitance (CLF-CHF) techniques, respectively, were used to determine the voltage and frequency dependent spectra of Nss and their lifetime (tau). Surface states (Nss), which are identified by admittance measurements, emerge at the M/S interlayer because of high capacitance and conductance values at low frequencies. This can also be explained by the Nss's ability to track ac signals well at lower frequencies. The normalized parallel conductance versus frequency (Gp/omega-f) plot under various biases shows a peak because of Nss existence. x-ray diffractometer (XRD) was used for structural investigation and the average crystal size (D) of the nanocrystals (CMAT) was found to be less than 0.34 nm by using the Debye-Scherer's equation.Item Improving The Quality Of Micro Holes Drilled With A Current Detection Plasma Arc Device(JOURNAL OF THE BRAZILIAN SOCIETY OF MECHANICAL SCIENCES AND ENGINEERING, 2024-10) Ic, Yusuf Tansel; Kocum, Cengiz; Atalay, Kumru Didem; Serdaroglu, Dilek Cokeliler; Akar, Gurel; Polat, Isil Yanki; Samsun, Berk; Caliskan, Sevde; Atmaca, Dicle Naz; Karayalcin, SerkanToday, microholes play a crucial role in many sectors. Microholes are used in fields such as aerospace, computer systems, and electronic and mechanical industries. In this paper, we improve the performance of the current sensing plasma arc device to create holes within the same diameter, appropriate delamination, and surface quality. In addition, we aim to improve the processing quality of the current sensing plasma arc device, which drills holes from the micron level to the millimeter level and creates microstructures on hard, durable, and inert materials such as glass and quartz. Additionally, we presented a multiobjective optimization model to reach the optimal factor levels to obtain the minimum hole diameter with minimum delamination. For this objective, we propose a design of an experiment-integrated goal programming model in this study. The optimal levels are 90 Watt, 18 Hz, 2.73 ms, and 11.6 cm for the parameter values Power, Frequency, Lead time, and Distance between the probes, respectively, to reach the optimal diameter (183 mu m) and delamination values (1.025).Item Can We Predict the Outcome of Varicocelectomy Based on the Duration of Venous Reflux?(2016) Goren, Mehmet Resit; Erbay, Gurcan; Ozer, Cevahir; Kayra, Mehmet Vehbi; Hasirci, Eray; https://orcid.org/0000-0002-2001-1386; https://orcid.org/0000-0002-1706-8680; https://orcid.org/0000-0001-6037-7991; https://orcid.org/0000-0002-7349-9952; https://orcid.org/0000-0002-4147-2966; 000373464600021; Y-6143-2019; AAK-5370-2021; AAK-8372-2021; AAI-7997-2021OBJECTIVE To investigate the outcome of varicocelectomy based on the duration of venous reflux (DVR) of the pampiniform plexus veins. MATERIALS AND METHODS In total, 138 patients with clinically palpable varicoceles were evaluated for DVR with color Doppler ultrasonography from May 2009 to August 2014. The DVR was defined as the DVR of a varicocele in the supine position during the Valsalva maneuver. Patients with bilateral, recurrent, or subclinical varicoceles; hormonal imbalances involving follicle-stimulating hormone, luteinizing hormone, or total testosterone; azoospermia; and intraoperative or postoperative complications were excluded. Of the 138 patients, 76 met the inclusion criteria. All patients were treated with subinguinal microscopic varicocelectomy. Restoration of all three semen parameters (concentration, motility, and morphology) to normal values 6 months postoperatively was considered to indicate treatment success. The patients were divided into those with a DVR of <4.5 seconds (Group 1) and >= 4.5 seconds (Group 2). RESULTS The mean age of the patients was 29.39 (+/- 6.03) years. No statistically significant relationship was found between the success rate and varicocele grade. The cutoff DVR value was calculated as 4.5 seconds using a receiver operating characteristics curve according to patients who underwent successful treatment. The success rates of Groups 1 and 2 were 40.0% and 88.2%, respectively (P = .0001). CONCLUSION The results of this analysis indicate that a DVR of >= 4.5 seconds predicts better outcomes of varicocelectomy. (C) 2016 Elsevier Inc.Item Effect of Dry Eye on Scheimpflug Imaging of the Cornea and Elevation Data(2017) Asena, Leyla; Alnors, Dilek D.; Cezairlioglu, Sefik; Boluk, Sefer Oguen; https://orcid.org/0000-0002-6848-203X; 28576215; E-5914-2016Objective: To evaluate the effect of dry eye on Scheimpflug imaging of the cornea and elevation data. Design: Prospective observational study. Participants: Scheimpflug images of 50 patients with dry eye who were being tested for eligibility for corneal refractive surgery were screened. Twelve eyes of 12 patients with abnormal Belin/Ambrosio enhanced ectasia display (BAD) anterior elevation difference were included in the study. The patients had no history of contact lens wear or any other sign of ectasia. Methods: Peak central corneal densitometry value, corneal volume, pachymetry at the thinnest point, and BAD anterior elevation difference value at the centre of the 9 mm zone were recorded before and after 4 weeks of dry eye treatment. Measurements were compared with the Wilcoxon signed rank test. Results: The mean corneal peak densitometry and volume were similar before and after therapy (p = 0.465 and p = 0.441, respectively). The mean anterior elevation difference value at the centre of the 9 mm zone before treatment (6.67 +/- 1.72 mu m) was significantly higher than the mean post-treatment value (4.00 +/- 1.48 mu m) (p = 0.002). The mean pachymetry at the thinnest location after treatment (548 +/- 11.0) was significantly higher than the pretreatment value (538 +/- 8.5) (p = 0.027). Conclusions: BAD anterior elevation differences and pachymetric measurements may be affected by ocular surface or tear film abnormalities associated with dry eye disease. Repeated evaluations after treatment may reveal normal results.Item Evaluation of maxillary trabecular microstructure as an indicator of implant stability by using 2 cone beam computed tomography systems and micro-computed tomography(2019) Kulah, Kivanc; Gulsahi, Ayse; Kamburoglu, Kivanc; Geneci, Ferhat; Ocak, Mert; Celik, H. Hamdi; Ozen, Tuncer; 30595501Objective. The aim of this study was to assess the trabecular microarchitecture of the maxilla by using cone beam computed tomography (CBCT) and micro-computed tomography (micro-CT) ex vivo. Study Design. Seventeen maxillary cadaver specimens were scanned by using micro-CT and CBCT devices. Samples were scanned with 2 CBCT devices at different voxel sizes (0.08, 0.125, and 0.160 mm for 3-D Accuitomo 170; 0.75 and 0.200 mm for Planmeca Promax 3-D Max). Morphometric parameters, such as bone volume/total volume (BV/TV) ratio, trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), trabecular number (Tb.N), and degree of anisotropy (DA) were assessed by using CTAnalyzer software. Bland-Altman limits of agreement and intraclass correlation coefficient (ICC) were performed to evaluate agreement between CBCT and micro-CT in consideration of measured morphometric parameters. Statistical significance was set at P < .05. Results. The BV/TV, Tb.Th, Tb.Sp, and DA values were higher for CBCT images compared with micro-CT images, whereas the Tb. N value was lower with CBCT images than with micro-CT images. The BV/TV and DA parameters showed the highest agreement between CBCT and micro-CT devices (ICC = 0.421 for BV/TV and ICC = 0.439 for DA; P < .01). Conclusions. The BV/TV and DA parameters measured on CBCT obtained at the smallest voxel size were found to be useful for the assessment of maxillary trabecular microstructure.Item The role of delineation education programs for improving interobserver variability in target volume delineation in gastric cancer(2017) Onal, Cem; Cengiz, Mustafa; Guler, Ozan C.; Dolek, Yemliha; Ozkok, Serdar; 0000-0002-2742-9021; 0000-0001-6908-3412; 28339289; D-5195-2014; AAC-5654-2020Objective: To assess whether delineation courses for radiation oncologists improve interobserver variability in target volume delineation for post-operative gastric cancer radiotherapy planning. Methods: 29 radiation oncologists delineated target volumes in a gastric cancer patient. An experienced radiation oncologist lectured about delineation based on contouring atlas and delineation recommendations. After the course, the radiation oncologists, blinded to the previous delineation, provided delineation for the same patient. Results: The difference between delineated volumes and reference volumes for pre-and post-course clinical target volume (CTV) were 19.8% (-42.4 to 70.6%) and 12.3% (-12.0 to 27.3%) (p = 0.26), respectively. The planning target volume (PTV) differences pre-and post-course according to the reference volume were 20.5% (-40.7 to 93.7%) and 13.1% (-10.6 to 29.5%) (p = 0.30), respectively. The concordance volumes between the pre-and post-course CTVs and PTVs were 467.1 +/- 89.2 vs 597.7 +/- 54.6cm(3) (p < 0.001) and 738.6 +/- 135.1 vs 893.2 +/- 144.6 cm(3) (p < 0.001), respectively. Minimum and maximum observer variations were seen at the cranial part and splenic hilus and at the caudal part of the CTV. The kappa indices compared with the reference contouring at pre- and post-course delineations were 0.68 and 0.82, respectively. Conclusion: The delineation course improved interobserver variability for gastric cancer. However, impact of target volume changes on toxicity and local control should be evaluated for further studies. Advances in knowledge: This study demonstrated that a delineation course based on current recommendations helped physicians delineate smaller and more homogeneous target volumes. Better target volume delineation allows proper target volume irradiation and preventing unnecessary normal tissue irradiation.