161 research outputs found
XRD and photoluminescence measurements of GaN grown on dome shaped patterned sapphire with different NH3 flow rates
No full textThe aim of the study is to understand the effects of NH3 flow rate in the initial part of high temperature (HT) GaN growth on structural and optical characteristics of the HT-GaN layer grown on dome shaped sapphire susbtrate by Metal Organic Chemical Vapor Deposition (MOCVD) system. High resolution x-ray diffraction (HRXRD) and photoluminescence (PL) measurements were performed to characterization the growing GaN epilayer. It is observed that the using of different NH3 flow rate in the initial part of HT-GaN growth has an effect on both full-width at half-maximum (FWHM) values obtained from HRXRD results and intensities of yellow luminescence peaks. It is seen that the FWHM values obtained from the symmetric (00.2) omega scan increased as the NH3 flow rates in the initial part of HT-GaN growth increased. It is demonstrated that the intensities of yellow luminescence peaks are very sensitive to NH3 flow rates in the initial part of HT-GaN growth
Growth kinetics of O-polar Be<sub>x</sub>Mg<sub>y</sub>Zn<sub>1-x-y</sub>O alloy: Role of Zn to Be and Mg flux ratio as a guide to growth at high temperature
No full textWe studied the effect of the substrate temperature, in the range from 450 degrees C to 500 degrees C, on the required Zn to (Be + Mg) flux ratio for plasma-assisted molecular beam epitaxy growth of O-polar BexMgyZn1-x-yO on (0001)-GaN/sapphire templates. Achievement of single-crystalline BexMgyZn1-x-yO with improved optical and structural qualities required relatively high substrate temperatures, which necessitated the Zn to (Be + Mg) flux ratio to be increased from 3.9 at 450 degrees C to 8.3 at 500 degrees C. This resulted in a reduction of Mg incorporation from 25% to 15% for a fixed Be content of similar to 3%. With increasing Zn to (Be + Mg) ratio, 15K photoluminescence energy for the dominant emission remained unchanged at around 3.75 eV and 3.55 eV for the samples grown at 475 degrees C and 500 degrees C, respectively. These findings readily suggest a kinetic limitation of Mg and Be incorporation into wurtzite BexMgyZn1-x-yO lattice, resulting in the formation of second phase due mainly to the enhanced surface mobility of Mg adatoms and, therefore, an increase in the probability of the formation of Mg-rich clusters. An increase in the in-plane lattice parameter, deduced from the Reflection High Energy Electron Diffraction, at the onset of the phase segregation suggests the formation of the wurtzite phase MgO rich alloy(s). Published by AIP Publishing.Air Force Office of Scientific Research (AFOSR) [FA9550-12-1-0094]; Scientific and Technological Research Council of Turkey (TUBITAK)This work was supported by Air Force Office of Scientific Research (AFOSR) under Grant No. FA9550-12-1-0094. Ismail Altuntas, acknowledges the Ph.D. Grant support from the Scientific and Technological Research Council of Turkey (TUBITAK). The authors are thankful to Dr. Monavarian for his help while providing (0001) GaN/sapphire template
MOVPE ile büyütülen GaN Epitabaka: Farklı Çekirdeklenme Tabakası Sıcaklığının Etkisi
No full textEffect of different nucleation layer temperatures (LT-GaN growth temperature) on the properties of the subsequent GaN epilayer grown by MOVPE is investigated. In-situ reflectance curves demonstrate that higher LT-GaN growth temperatures cause fast coalescence (shorter transition time) of GaN nucleation islands. Both photoluminescence (PL) and high-resolution x-ray diffraction (HRXRD) are used to demonstrate the influence of LT-GaN growth temperature on optical and structural properties of subsequent GaN epilayer, respectively. It is observed that the change of LT-GaN growth temperature has an effect on both full-width at half-maximum (FWHM) values obtained from the results of HRXRD measurement and yellow luminescence peak intensity. It is seen that the yellow luminescence peak intensities for samples alter with LT-GaN growth temperature
Estimation of Exterior Parameters of Sensor Combination for Efficient 3D Modeling
No full textISPRS-Commission V Mid-Term Symposium on Close Range Image Measurement Technique -- JUN 21-24, 2010 -- Newcastle upon Tyne, ENGLANDLaser scanning is the latest method to collect 3D spatial data and modelling. It becomes more and more popular in engineering applications such as 3D modeling, deformation analysis, reverse engineering and urban planning. However, laser scanners are not sufficient on their own for 3D surveying and modeling. It should be used together with the photogrammetric data especially in the orientation of point clouds, measurement of the non-scanning areas, and texture mapping. This task needs the combination of range sensor and image sensor. The sensor combination like this is a very efficient and flexible system for close-range measurement applications. Most of the laser scanners include integrated camera but most of them are low resolution and they can not be removed independent from the scanner. Therefore high resolution camera should be mounted to the laser scanner. In this study we consider mounting a camera onto laser scanner and estimating exterior parameters with strong control methods. We also made experimental studies by using exterior parameters.ISPRS CommissScientific and Technological Research Council of Turkey ( TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); "Foreign Research Scholarship Program" to Cihan ALTUNTAS; Vienna University of Technology; Scientific Research Found of The Selcuk University ( BAP)We would like to thank The Scientific and Technological Research Council of Turkey ( TUBITAK) for the financial support they have provided as a part of "Foreign Research Scholarship Program" to Cihan ALTUNTAS to the carried out this study in Vienna University of Technology. In addition author Cihan ALTUNTAS thanks Scientific Research Found of The Selcuk University ( BAP) to financial support to attend this scientific event
The hydrostatic pressure and temperature effects on hydrogenic impurity binding energies in GaAs/InxGa1-xAs/GaAs square quantum well
No full textWe have calculated the ground state binding energy using variational methods and the effective mass approximation for the hydrogenic impurity in square quantum well structure made up of GaAs/InGaAs/GaAs epilayers under the action of hydrostatic pressure and temperature for different well widths and barrier heights. The effects of the variation of hydrostatic pressure and temperature can be summarized as follows; impurity binding energy is a negligibly decreasing function of temperature for fixed pressure and is an increasing function of pressure for fixed temperature. (C) 2015 Elsevier Ltd. All rights reserved
The Effect of Si (111) Substrate Surface Cleaning on Growth Rate and Crystal Quality of MOVPE Grown AlN
No full textIn this work, the effect of Si (111) substrate surface cleaning by RCA (Radio Corporation of America) method on growth rate and crystalline quality of epitaxially grown AlN thin films by MOVPE (Metal Organic Vapor Phase Epitaxy) technique is investigated. In situ reflectance system and high resolution X-ray diffraction (HRXRD) technique are used for the analysis of growth rate and crystal quality of epitaxial AlN layers, respectively. Also, The Raman measurement is done to show the effect of the RCA cleaning procedure on the position of the peaks that occurred in the Raman spectra. The results have shown that the surface cleaning of Si (111) substrate by the RCA method removes the oxide layer formed on the surface, also helps to decrease the parasitic reactions and increases the adatom efficiency, results in an increased growth rate of the AlN layer. Besides, surface cleaning of Si (111) substrate by the RCA method has reduced the FWHM value similar to 5% for omega-2 theta scan and similar to 60% for omega scan of AlN epilayer, indicating an improvement in crystal quality.TUBITAK [117F339, 118F425]; Scientific Research Project Fund of Sivas Cumhuriyet University [M-772]This study is supported by TUBITAK under the project numbers 117F339, 118F425 and by the Scientific Research Project Fund of Sivas Cumhuriyet University under the Project number M-772. The authors acknowledge the usage of the Nanophotonics Research and Application Center at Sivas Cumhuriyet University (CUNAM) facilities
Reactions of 4-(p-methylbenzoyl)-5(p-methylphenyl)furan-2,3-dione with various anilides
No full text4-(p-Methylbenzoyl)-5-(p-methylphenyl)furan-2,3-dione (1) reacts with acetanilides (3a-f) under different conditions and gives open-chain dibenzoylacetic acid derivatives 4a,b, 5c-f It has been demonstrated that with the variation in reaction conditions, the reaction changes leading to different products. All the newly synthesized compounds were characterized by elemental analysis, IR, H-1 and C-13 NMR spectral data. All were compared with their previous analogues
The use of high-dose acyclovir in patients with hematological malignancies who develop herpes virus infections: Is it really safe?
No full textConnective tissue and its growth factor CTGF distinguish the morphometric and molecular remodeling of the bladder in a model of neurogenic bladder
No full textAltuntas CZ, Daneshgari F, Izgi K, Bicer F, Ozer A, Sakalar C, Grimberg KO, Sayin I, Tuohy VK. Connective tissue and its growth factor CTGF distinguish the morphometric and molecular remodeling of the bladder in a model of neurogenic bladder. Am J Physiol Renal Physiol 303: F1363-F1369, 2012. First published September 19, 2012; doi:10.1152/ajprenal.00273.2012.-We previously reported that mice with experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS), develop profound urinary bladder dysfunction. Because neurogenic bladder in MS patients causes marked bladder remodeling, we next examined morphometric and molecular alterations of the bladder in EAE mice. EAE was created in female SJL/J mice by immunization with the p139-151 encephalitogenic peptide of myelin proteolipid protein in complete Freund's adjuvant, along with intraperitoneal injections of Bordetella pertussis toxin. Seventy days after immunization, mice were scored for the level of neurological impairment and then killed. Spinal cord sections were assessed for demyelination, inflammation, and T cell infiltration; the composition of the bladder tissue was measured quantitatively; and gene expression of markers of tissue remodeling and fibrosis was assessed. A significant increase in the bladder weight-to-body weight ratio was observed with increasing neurological impairment, and morphometric analysis showed marked bladder remodeling with increased luminal area and tissue hypertrophy. Despite increased amounts of all tissue components (urothelium, smooth muscle, and connective tissue), the ratio of connective tissue to muscle increased significantly in EAE mice compared with control mice. Marked increases in mRNA expression of collagen type I alpha(2), tropoelastin, transforming growth factor-beta 3, and connective tissue growth factor (CTGF) were observed in EAE mice, as were decreased levels of mRNAs for smooth muscle myosin heavy chain, nerve growth factors, and muscarinic and purinergic receptors. Our results suggest that bladder remodeling corresponding to EAE severity may be due to enhanced expression of CTGF and increased growth of connective tissue
Audiological evaluation of hearing levels in patients diagnosed with migraine
No full textIntroduction: Based on the hypothesis that neurovascular events involving in the pathophysiology of migraine can cause hearing loss by influencing blood flow of inner ear, it was aimed to determine whether migraine with or without aura in our clinics patients are at risk for hearing loss by assessing hearing levels via a high-frequency audiometry, acoustic reflex and transient otoacoustic emission responses; to discriminate whether hearing loss is cochlear or retrocochlear originated, if present; and to evaluate whether or not migraine treatment affect hearing level in patients received treatment for migraine in this study. Materials and Methods: The study included patients who were diagnosed as migraine between December 2011 and December 2012 at Neurology Department of Cumhuriyet University, Medicine School according to ICD-II classification and accepted to receive medical therapy. In all patients, hearing levels were measured at baseline and after treatment by using high-frequency audiometry, transient otoacoustic emission and acoustic reflex tests. Results: In the present study, hearing thresholds measured in the right ear was normal in migraine patients with or without aura at baseline, while mild hearing loss was detected in right ear at the frequency of 500 Hz after treatment when hearing thresholds at different frequencies were compared. This difference was significant (P 0, 05). Conclusion: Differently from literature, hearing loss in our patients developed at lower frequencies and after treatment. The results we obtained from our study also presented that there might be a relationship between migraine disease and sensorineural hearing loss
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