Photoluminescence of near-lattice-matched GaN/AlInN quantum wells grown on free-standing GaN and on sapphire substrates

Near-lattice-matched GaN/Al1−xInxN single quantum wells, grown using both free-standing GaN and conventional GaN-on-sapphire substrates, are studied by photoluminescence (PL) and PL excitation spectroscopies. PL spectra distinguish luminescence originating in the wells, barriers, and underlying GaN buffer layers. The spectra also reveal significant differences between structures grown simultaneously on the different substrates. The quantum well transition energy decreases as the well width increases due to the intense in-built electric fields, estimated to be 3.0±0.5 MeV/cm, that persist in strain free GaN/Al1−xInxN. Screening of these fields is studied using the excitation power dependence of the P

Photoluminescence and phonon satellites of single InGaN/GaN quantum wells with varying GaN cap thickness

Variations in thickness of the GaN caps above single InGaN quantum wells have been studied using photoluminescence spectroscopy. Data are presented from two series of samples designed to promote energy transfer to luminescent species on the surface. Improvements in the optical properties as the GaN cap thickness increases from 2.5 to 15 nm are accompanied by clear changes in the intensity of the LO-phonon satellites. Analysis of the strength of successive phonon satellites and the associated Huang-Rhys factors indicates that the amount of localization of the excitons is increased for the thinner cap samples. Surface depletion fields are also considered

Fishes of the Eastern Johor Strait

© National University of Singapore. We record the presence of 435 fish species from the Eastern Johor Strait based on our fieldwork, a review of the existing literature, and an examination of photographs and museum specimens. Four species are recorded for the first time from the waters of Singapore: Pseudorhombus elevatus (Paralichthyidae), Heteromycteris hartzfeldii (Soleidae), Nuchequula manusella (Leiognathidae) and Johnius carouna (Sciaenidae)

Inducing safer oblique trees without costs

Decision tree induction has been widely studied and applied. In safety applications, such as determining whether a chemical process is safe or whether a person has a medical condition, the cost of misclassification in one of the classes is significantly higher than in the other class. Several authors have tackled this problem by developing cost-sensitive decision tree learning algorithms or have suggested ways of changing the distribution of training examples to bias the decision tree learning process so as to take account of costs. A prerequisite for applying such algorithms is the availability of costs of misclassification. Although this may be possible for some applications, obtaining reasonable estimates of costs of misclassification is not easy in the area of safety. This paper presents a new algorithm for applications where the cost of misclassifications cannot be quantified, although the cost of misclassification in one class is known to be significantly higher than in another class. The algorithm utilizes linear discriminant analysis to identify oblique relationships between continuous attributes and then carries out an appropriate modification to ensure that the resulting tree errs on the side of safety. The algorithm is evaluated with respect to one of the best known cost-sensitive algorithms (ICET), a well-known oblique decision tree algorithm (OC1) and an algorithm that utilizes robust linear programming

Compact graphene mode-locked wavelength-tunable erbium-doped fiber lasers: from all anomalous dispersion towards all normal dispersion

Soliton operation and soliton wavelength tuning of erbium-doped fiber lasers mode locked with atomic layer graphene was experimentally investigated under various cavity dispersion conditions. It was shown that not only wide range soliton wavelength tuning but also soltion pulse width variation could be obtained in the fiber lasers. Our results show that the graphene mode locked erbium-doped fiber lasers provide a compact, user friendly and low cost wavelength tunable ultrahsort pulse source

PRODUCTION OF MEDIUM CHAIN LENGTH POLYHYDROXYALKANOATES FROM OLEIC ACID USING Pseudomonas putida PGA1 BY FED BATCH CULTURE

Bacterial polyhydroxyalkanoates (PHAs) are a class of polymers currently receiving much attention because of theirpotential as renewable and biodegradable plastics. A wide variety of bacteria has been reported to produce PHAsincluding Pseudomonas strains. These strains are known as versatile medium chain length PHAs (PHAs-mcl) producersusing fatty acids as carbon source. Oleic acid was used to produce PHAs-mcl using Pseudomonas putida PGA 1 bycontinuous feeding of both nitrogen and carbon source, in a fed batch culture. During cell growth, PHAs alsoaccumulated, indicating that PHA production in this organism is growth associated. Residual cell increased until thenitrogen source was depleted. At the end of fermentation, final cell concentration, PHA content, and productivity were30.2 g/L, 44.8 % of cell dry weight, and 0.188 g/l/h, respectively.Keywords: Biodegradable plastics, medium-chain-length polyhydroxyalkanoates (PHAs-mcl), oleic acid, Pseudomonasputida PGA 1, fed batch fermentatio

Preliminary Studies of Porous GaNbased Dye-Sensitized Solar Cells

This work presents the preliminary studies of porous gallium nitride (GaN) based dye-sensitized solar cells (DSSC). Porous GaN was fabricated using photo-assisted electrochemical etching (PEC), then characterized in terms of its morphological, structural, optical and vibrational aspects. Next, the sample underwent sensitization through immersing in N719 ruthenium based dye for one day. For the DSSC assembly, the dyed porous GaN would serve as anode while platinum (Pt) coated fluorinedoped tin oxide (FTO) glass being the cathode. A thin glass spacer separates the anode/cathode, while triiodide/iodide redox electrolyte would fill the gap between them. Current density-voltage (J-V) curves was obtained under light illumination and used to determine the essential electrical parameters of the DSSC. The open circuit potential <Voc). short-circuit current density (Jsc). and efficiency (TJ) for the aforementioned were 638.8 mV, 0.81 mA/cm2 , and 0.2% respectively. Aside from that, similar works have been repeated here for as-grown GaN, however, the resultant efficiency was ten times lower than that of porous GaN

Hydrologic Modeling and Delineation of Calumpang River Watershed using GIS and Hydrologic Model System

The Calumpang Bridge in CALABARZON Region, Southern Luzon Philippines did not withstand the river current brought by Super Typhoon Glenda (Rammasun) on July 2014, causing the destruction of one-third of the bridge, thus resulting to traffic congestion and economic distress for the residents and businessmen. This paper aims to create a calibrated hydrological model. Specifically, it focuses on delineating watershed, simulation based on observed flow data and validation that will be the basis for flood risk map for the river. The watershed has been delineated and it is calibrated, the basin was modeled using Hydrologic Model System and GIS Applications to determine hydrologic parameters which have spatial characteristic and to compute the peak Discharge and loss infiltration. The model delineated by the use of GIS software has been hydrologically corrected. The model describes the correlation of the rainfall, losses, time of concentration, Storage factor and amount of discharge. It shows that the amount of Rainfall at a given time dictates the amount of discharge the watershed generates. The higher the rainfall amount, the higher the discharge. The model was validated using Percentage Error and Rational Method, and due to the accuracy of the validated model, it provides a promising approach to Bridge Structural Design and Flood Risk Map Generation

Notes on a paper of Mess

These notes are a companion to the article "Lorentz spacetimes of constant curvature" by Geoffrey Mess, which was first written in 1990 but never published. Mess' paper will appear together with these notes in a forthcoming issue of Geometriae Dedicata.Comment: 26 page

Ambitions of a global city: Arts, culture and creative economy in 'Post-Crisis' Singapore

10.1080/10286632.2011.639876International Journal of Cultural Policy183279-29