Thermal stability of electron traps in GaN grown by metalorganic chemical vapor deposition

Deep level transient spectroscopy was used to investigate the thermal stability of electron traps in n-type GaN grown by metalorganic chemical vapor deposition. The concentration of traps at 160 and at 500K increased more than fivefold over the course of several 700Kanneal cycles, while a peak at 320K increased by a factor of only 1.19. The increase in the trap concentration with repeated annealing might be due to a mobile trap or loss of passivant. Hydrogen is very likely present in high concentration in the epilayer, and its passivating effects may be lost with annealing

Three-dimensional modelling and morphometric investigation of computed tomography images of brown bear’s (Ursus arctos) ossa cruris (Zeugopodium)

Background: This study was aimed to examine the detailed morphometrical and morphological characteristics of the bone by creating three-dimensional images through multidetector computed tomography images of ossa cruris in brown bears.Materials and methods: Four brown bear ossa cruris were used in the study.Results: It was observed that tibia and fibula articulated at proximal and distal epiphysis and they combined, and ossa cruris were shaped in this way. Cochlea tibiae were determined to be sagittally oriented. The length of the tibia was determined to be 268.97 mm and 266.32 mm at right and left sides, respectively. The length of the fibula was determined to be 249.16 mm and 250.19 mm on average at the right and left sides, respectively. In consequence of the correlation analysis, statistical relationships at different rates were detected between themeasured values.Conclusions: Detailed anatomical examinations are very important in terms of determining the similarities and differences of bear bones with those of the other species in the order Carnivora. Therefore, it is thought that this study will reveal detailed characteristics of ossa cruris of bears and provide data for further studies on archaeological and forensic sciences

Determination of periodic deformation from InSAR results using the FFT time series analysis method in Gediz Graben

Permanent Scatterers (PS) point velocities obtained by the interferometric synthetic aperture radar (InSAR) method are generally determined using the linear regression model, which ignores periodic and seasonal effects. In this study, software was developed that can detect periodic effects by applying fast Fourier transformation (FFT) time series analysis to InSAR results. Using the FFT time series analysis, the periodic components of the surface movements at the PS points were determined, and then the annual velocity values free from periodic effects were obtained. The study area was chosen as the Gediz Graben, a tectonically active region where aseismic surface deformations have been observed in recent years. As a result, using the developed method, seasonal effects were successfully determined with the InSAR method at the PS points in the study area with a period of 384 days and an average amplitude of 19 mm. In addition, groundwater level changes of a water well in the region were modeled, and 0.93 correlation coefficient values were calculated between seasonal InSAR displacement values and water level changes. Thus, using the developed methodology, the relationship between the tectonic movement in the Gediz Graben in Turkey and the seasonal movements and the change in the groundwater level was determined

Effect of n+-GaN subcontact layer on 4H–SiC high-power photoconductive switch

High-power photoconductive semiconductor switching devices were fabricated on 4H–SiC. In order to prevent current crowding, reduce the contact resistance, and avoid contact degradation, a highly n-doped GaN subcontact layer was inserted between the contact metal and the high resistivity SiC bulk. This method led to a two orders of magnitude reduction in the on-state resistance and, similarly, the photocurrent efficiency was increased by two orders of magnitude with the GaN subcontact layer following the initial high current operation. Both dry etching and wet etching were used to remove the GaN subcontact layer in the channel area. Wet etching was found to be more suitable than dry etching

Effectiveness of TiN porous templates on the reduction of threading dislocations in GaN overgrowth by organometallic vapor-phase epitaxy

We report on the reduction of threading dislocations in GaN overlayers grown by organometallic vapor phase epitaxy on micro-porous TiN networks. These networks were obtained by in situannealing of thin Ti layers deposited in a metalization chamber, on the (0001) face of GaN templates. Observations by transmission electron microscopy indicate dislocation reduction by factors of up to 10 in GaN layers grown on TiN networks compared with the control GaN.X-ray diffraction shows that GaNgrown on the TiN network has a smaller (102) plane peak width (4.6 arcmin) than the control GaN (7.8 arcmin). In low temperature photoluminescence spectra, a narrow excitonic full-width-at-half-maximum of 2.4 meV was obtained, as compared to 3.0 meV for the control GaN, confirming the improved crystalline quality of the overgrown GaN layers

Cardiogram of the park: quantitative analysis of walking scenarios of Trakų Vokė historic park

In this research, the concept of isovist [1,6] was employed to analyze spaces of the park as a container and catalyser of human activities and experiences in quantitative terms. The concept of the isovist defines the visual environment as a system of objects that structures the light as a source of stimuli for human perception. Trakų Vokė ensemble was selected as a case study object to test this quantitative approach towards historic park analysis. Methods of the research include a literature review on specific characteristics of Trakų Vokė ensemble, observation on site, analysis of available maps and satellite images, development of linear drawing of the park using AutoCAD, modelling using Isovist_App and ESRI ArcMap software, analysis, and discussion of results. The research has demonstrated that the results of the isovist and visual graph-based analysis reflect the observed spatial features of Trakų Vokė Park quite well and can be used for various purposes, including a more detailed description of valuable features of heritage objects, a detailed comparison between different parks, simulative reconstruction of the character of the historical park in the past based on historical data, maintenance and management of the park, parametric design of landscape spaces, etc

Stellar ages and convective cores in field main-sequence stars: first asteroseismic application to two Kepler targets

Using asteroseismic data and stellar evolution models we make the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence life time is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.Comment: 46 pages, 10 figures, ApJ accepte

Seroepidemiology of Toxoplasma gondii infection in patients with liver disease in eastern China

The role of the protozoan parasite Toxoplasma gondii in the pathogenesis of liver disease has recently gained much interest. The aim of this study was to determine the prevalence and risk factors associated with T. gondii infection in patients with liver disease from three cities in Shandong and Henan provinces, China. A case–control study was conducted from December 2014 to November 2015 and included 1142 patients with liver disease and 1142 healthy controls. Serum samples were collected from all individuals and were examined with enzyme-linked immunosorbent assay for the presence of anti-T. gondii IgG and IgM antibodies. Information on the demographics, clinical, and lifestyle characteristics of the participants was collected from the medical records and by the use of a questionnaire. The prevalence of anti-T. gondii IgG was 19·7% in patients with liver disease compared with 12·17% in the controls. Only 13 patients had anti-T. gondii IgM antibodies compared with 12 control individuals (1·14% vs. 1·05%, respectively). The highest seroprevalence was detected in patients with liver cancer (22·13%), followed by hepatitis patients (20·86%), liver cirrhosis patients (20·42%), and steatosis patients (20%). Multivariate logistic regression analysis indicated that consumption of raw meat (odds ratio (OR) = 1·32; 95% confidence interval (CI) 1·01–1·71; P = 0·03) and source of drinking water from wells (OR = 1·56; 95% CI 1·08–2·27; P = 0·01) were independent risk factors for T. gondii infection in liver disease patients. These findings indicate that T. gondii infection is more likely to be present in patients with liver disease. Therefore, efforts should be directed toward health education of populations at high risk of T. gondii infection and measures should be taken to protect vulnerable patients with liver disease

Magnetic Order in YBa2_2Cu3_3O6+x_{6+x} Superconductors

Polarized and unpolarized neutron diffraction has been used to search for magnetic order in YBa$_2$Cu$_3$O$_{6+x}$ superconductors. Most of the measurements were made on a high quality crystal of YBa$_2$Cu$_3$O$_{6.6}$. It is shown that this crystal has highly ordered ortho-II chain order, and a sharp superconducting transition. Inelastic scattering measurements display a very clean spin-gap and pseudogap with any intensity at 10 meV being 50 times smaller than the resonance intensity. The crystal shows a complicated magnetic order that appears to have three components. A magnetic phase is found at high temperatures that seems to stem from an impurity with a moment that is in the $a$-$b$ plane, but disordered on the crystal lattice. A second ordering occurs near the pseudogap temperature that has a shorter correlation length than the high temperature phase and a moment direction that is at least partly along the c-axis of the crystal. Its moment direction, temperature dependence, and Bragg intensities suggest that it may stem from orbital ordering of the $d$-density wave (DDW) type. An additional intensity increase occurs below the superconducting transition. The magnetic intensity in these phases does not change noticeably in a 7 Tesla magnetic field aligned approximately along the c-axis. Searches for magnetic order in YBa$_2$Cu$_3$O$_{7}$ show no signal while a small magnetic intensity is found in YBa$_2$Cu$_3$O$_{6.45}$ that is consistent with c-axis directed magnetic order. The results are contrasted with other recent neutron measurements.Comment: 11 pages with 10 figure