Formation of high-quality Ag-based ohmic contacts to p-type GaN

Low resistance and high reflectance ohmic contacts on p-type GaN were achieved using an Ag-based metallization scheme. Oxidation annealing was the key to achieve ohmic behavior of Ag-based contacts on p-type GaN. A low contact resistivity of similar to 5x10(-5) Omega cm(2) could be achieved from Me (=Ni, Ir, Pt, or Ru)/Ag (50/1200 angstrom) contacts after annealing at 500 degrees C for 1 min in O(2) ambient. Oxidation annealing promoted the out-diffusion of Ga atoms from the GaN layer, and Ga atoms dissolved in the in-diffused Ag layer with the formation of Ag-Ga solid solution, resulting in ohmic contact formation. Using Ru/Ni/Au (500/200/500 angstrom) overlayers on the Me/Ag contacts, the excessive incorporation of oxygen molecules into the contact interfacial region, and the out-diffusion and agglomeration of Ag, were effectively prevented during oxidation annealing. As a result, a high reflectance of 87.2% at the 460 nm wavelength and a smooth surface morphology could be obtained simultaneously. (C) 2008 The Electrochemical Society.open111618sciescopu

FE Modeling Methodology for Load Analysis and Preliminary Sizing of Aircraft Wing Structure

It is a critical part at the basic design phase of aircraft structural design to build a finite element model and it will have a direct impact on time and cost for airframe structure development. In addition, the objective of finite element model will be varied depending on each design review phase and the modelling methodology varied accordingly. In order to build an effective and economic finite element model, it is required to develop adequate level of modelling methodology based on each design phase and its objectives. Therefore, in this paper, the finite element modeling methodology was presented for internal load analysis of wing structure of multi-spar type military aircraft, load path evaluation and initial sizing of wing structure. All structures reflected mechanical function and at the same time, idealized to achieve easy and conservative result of internal load evaluation. Through analysis of various loads, it was confirmed that the finite element modeling suggested in this paper and initial sizing method could be applied to internal load analysis of wing structure and initial sizing

Investigating soil change in Edgeroi, New South Wales using pedogenon mapping framework

The impact of anthropogenic activities on soil has been significant in the last few hundred years, surpassing that of natural processes that occurred over thousands of years. Soil organic carbon (SOC) is especially vulnerable to anthropogenic forces and is critical to support soil functions such as nutrient and water cycling, crop production, and habitat for ground biodiversity. It is hence crucial to understand the current SOC status and predict how it has changed due to human influences. However, assessing changes in soil is challenging due to the various factors involved in soil formation. This thesis studies the SOC change in the Edgeroi area of New South Wales since European settlement using the pedogenon mapping concept. Pedogenon divides a landscape into unique soil entities based on homogeneous soil-forming factors, distinguishing soils that have been less affected by human activities (genosoil) and those that have been intensely affected (phenosoils). The primary hypothesis of this thesis is that pedogenon mapping can effectively stratify the landscape and be used to estimate soil change. To produce pedogenon classes, a parent material map of the study area was produced using interpretation and machine-learning methods. An unsupervised classification of spatial layers representing soil-forming factors was then used to create the pedogenon map. Within each pedogenon, genosoil and phenosoil areas were identified using land use data. Multivariate data analysis confirmed each pedogenon has unique soil properties from the surface down to 1 m. SOC data from genosoil and phenosoil areas were then compared and mapped to investigate soil change. The results showed the soil property variation under phenosoil is half that of genosoil due to agricultural practices. Additionally, this approach enables the mapping of SOC sequestration potential using mineral-associated OC contents. This thesis improves the current digital soil mapping approach for assessing soil change

Tracking the Mn diffusion in the carbon-supported nanoparticles through the collaborative analysis of atom probe and evaporation simulation

Carbon-supported nanoparticles have been used widely as efficient catalysts due to their enhanced surface-to-volume ratio. To investigate their structure-property relationships, acquiring 3D elemental distribution is highly required. Here, the carbon-supported Pt, PtMn alloy, and ordered Pt3Mn nanoparticles are synthesized and analyzed with atom probe tomography as model systems. The significant difference of Mn distribution after the heat-treatment was found. Finally, the field evaporation behavior of the carbon support was discussed and each acquired reconstruction was compared with computational results from the evaporation simulation. This paper provides a guideline for studies using atom probe tomography on the heterogeneous carbon-nanoparticle system that leads to insights toward to a wide application in carbon-supported nano-catalysts

Indium as an efficient ohmic contact to N-face n-GaN of GaN-based vertical light-emitting diodes

We propose indium (In), a low work function and nitride-forming element, as an efficient ohmic contact layer to N-face n-GaN. While conventional Al-based ohmic contacts show severe degradation after annealing at 300 C, In-based ohmic contacts display considerable improvement in contact resistivity. The annealing-induced enhancement of ohmic behavior in In-based contacts is attributed to the formation of an InN interfacial layer, which is supported by x-ray photoemission spectroscopy measurements. These results suggest that In is of particular importance for application as reliable ohmic contacts to n-GaN of GaN-based vertical light-emitting diodes.open3

The effect of beta1-adrenergic receptor gene polymorphism on prolongation of corrected QT interval during endotracheal intubation under sevoflurane anesthesia

BACKGROUND: The hemodynamic responses to endotracheal intubation are associated with sympathoadrenal activity. Polymorphisms in the beta1-adrenergic receptor (β(1)AR) gene can alter the pathophysiology of specific diseases. The aim of this study is to investigate whether the Ser49Gly and Arg389Gly polymorphism of the β(1)AR gene have different cardiovascular responses during endotracheal intubation under sevoflurane anesthesia. METHODS: Ninety-one healthy patients undergoing general anesthesia were enrolled. Patients underwent slow inhalation induction of anesthesia using sevoflurane in 100% oxygen. Vecuronium 0.15 mg/kg was given for muscle relaxation. Endotracheal intubation was performed by an anesthesiologist. The mean arterial pressure (MAP), heart rate (HR), and the corrected QT (QTc) interval were measured before induction, before laryngoscopy, and immediately after tracheal intubation. Genomic DNA was isolated from the patients' peripheral blood and then evaluated for the β(1)AR-49 and β(1)AR-389 genes using an allele-specific polymerase chain reaction method. RESULTS: No differences were found in the baseline values of MAP, HR, and the QTc interval among β(1)AR-49 and β(1)AR-389, respectively. In the case of β(1)AR-49, the QTc interval change immediately after tracheal intubation was significantly greater in Ser/Ser genotypes than in Ser/Gly genotypes. No differences were observed immediately after tracheal intubation in MAP and HR for β(1)AR-49 and β(1)AR-389. CONCLUSIONS: We found an association between the Ser49 homozygote gene of β(1)AR-49 polymorphism and increased QTc prolongation during endotracheal intubation with sevoflurane anesthesia. Thus, β(1)AR-49 polymorphism may be useful in predicting the risk of arrhythmia during endotracheal intubation in patients with long QT syndrome.ope

A NUMERICAL STUDY ON THE OPEN WATER PERFORMANCE OF A PROPELLER WITH SINUSOIDAL PITCH MOTION

When a ship operates in waves, the ship moves with 6 degrees-of-freedom, and a propeller at the stern of the ship cannot avoid moving due to the ship motion. Therefore, it is important to analyse the propulsion performance while considering the ship motion in waves for efficient ship operation. The pitch motion of the ship has a dominant effect on the variation of the propeller performance and results in sinusoidal pitch motion of the propeller. In this study, a numerical analysis was done using a KP458 model propeller with a diameter of 10 cm, which was designed for the KLVCC2 body plan. The propeller performance was calculated using computational fluid dynamics (CFD) at several constant tilt angles. Numerical simulations were then conducted with sinusoidal pitch motion in several conditions of varying pitch angle. The variations of the thrust and torque of the propeller in sinusoidal pitch motion were compared with the results obtained in constant tilt angles

Study of a Vocal Feature Selection Method and Vocal Properties for Discriminating Four Constitution Types

The voice has been used to classify the four constitution types, and to recognize a subject's health condition by extracting meaningful physical quantities, in traditional Korean medicine. In this paper, we propose a method of selecting the reliable variables from various voice features, such as frequency derivative features, frequency band ratios, and intensity, from vowels and a sentence. Further, we suggest a process to extract independent variables by eliminating explanatory variables and reducing their correlation and remove outlying data to enable reliable discriminant analysis. Moreover, the suitable division of data for analysis, according to the gender and age of subjects, is discussed. Finally, the vocal features are applied to a discriminant analysis to classify each constitution type. This method of voice classification can be widely used in the u-Healthcare system of personalized medicine and for improving diagnostic accuracy