bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seasonal variation and environmental predictors of exhaled nitric oxide in children with asthma
Authors: Spanier Adam J. , Hornung Richard W. , Kahn Robert S. , Lierl Michelle B. , Lanphear Bruce P. 
Published: April 2008

AbstractThe fraction of exhaled nitric oxide (FeNO), a measure of airway inflammation, shows promise as a noninvasive tool to guide asthma management, but there is a paucity of longitudinal data about seasonal variation and environmental predictors of FeNO in children. The objective of this project was to evaluate how environmental factors affect FeNO concentrations over a 12‐month study period among children with doctor diagnosed asthma. We conducted a prospective cohort study of 225 tobacco‐smoke exposed children age 6–12 years with doctor‐diagnosed asthma including measures of FeNO, medication use, settled indoor allergens (dust mite, cat, dog, and cockroach), and tobacco smoke exposure. Baseline geometric mean FeNO was 12.4 ppb (range 1.9–60.9 ppb). In multivariable analyses, higher baseline FeNO levels, atopy, and fall season were associated with increased FeNO levels, measured 6 and 12 months after study initiation, whereas inhaled steroid use, summer season, and increasing nicotine exposure were associated with lower FeNO levels. In secondary analyses of allergen sensitization, only sensitization to dust mite and cat were associated with increased FeNO levels. Our data demonstrate that FeNO levels over a year long period reflected baseline FeNO levels, allergen sensitization, season, and inhaled steroid use in children with asthma. These results indicate that FeNO levels are responsive to common environmental triggers as well as therapy for asthma in children. Clinicians and researchers may need to consider an individual's baseline FeNO levels to manage children with asthma. Pediatr Pulmonol. 2008; 43:576–583. © 2008 Wiley‐Liss, Inc.
High temperature Ohmic contacts to p‐type GaN for use in light emitting applications
Authors: Voss L. F. , Stafford L. , Hlad M. , Gila B. P. , Abernathy C. R. , Pearton S. J. , Ren F. , Kravchenko I. 
Published: April 2008

AbstractAchieving low resistance contacts to p‐type Gallium Nitride is a critical requirement for the fabrication of reliable AlGaN/InGaN laser diodes and nitride‐based light‐emitting diodes (LEDs). Three separate groups of materials are examined. The first is a family of borides, including W2B, W2B5, CrB2, TiB2, and ZrB2; the second is a group of nitrides, TaN, TiN, and ZrN; and the third is the refractory metal Ir. Using these materials both directly on the surface of p‐GaN as well as a diffusion barrier for Ni/Au‐based Ohmic contacts, specific contact resistances as low as ∼1x10–4 Ω.cm2 have been achieved. In addition, the boride and iridium based contacts display superior aging characteristics with minimal degradation of the contact resistance and of the turn on voltage of light emitting diodes after extended periods at 350 °C. The reasons for the discrepancies in performance of different materials is examined through the use of IV curves as well as Auger Electron Spectroscopy (AES) depth profiles. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First all‐HVPE grown InGaN/InGaN MQW LED structures for 460‐510 nm
Authors: Syrkin A. , Ivantsov V. , Kovalenkov O. , Usikov A. , Dmitriev V. , Liliental‐Weber Z. , Reed M. L. , Readinger E. D. , Shen H. , Wraback M. 
Published: April 2008

AbstractIn this paper we report on first InGaN‐based light emitting structures grown by hydride vapour phase epitaxy (HVPE). InGaN layers and multi layer InGaN/InGaN epitaxial structures were grown on GaN/sapphire template substrates and characterized. InN content in the InGaN layers was varied from 5 to 35 mol.%. Thickness of InGaN layers was controlled from 10 nm to 2 microns. Density of treading dislocations in the InGaN layers was estimated to be in the 109 cm–2 range. X‐ray diffraction measurements and transmission electron microscopy data confirmed a formation of InGaN/InGaN superlattice structures. Light emitting diode epitaxial wafers were fabricated by HVPE deposition of n‐type InGaN layers and multi layer structures on p‐type GaN template substrates. Depending on InN content in the InGaN light emitting regions, peak electroluminescence wavelength varied from 450 to 510 nm. Results of material characterization are reported. Advantages of the proposed upside down LED configuration and future applications of HVPE to grow InGaN layers and structures are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
InN nanorods and nanowires grown on different substrates
Authors: Liliental‐Weber Z. , Hawkridge M. , Mangum J. , Kryliouk O. 
Published: April 2008

AbstractTransmission Electron Microscopy was applied to study InN nanorods grown by non‐catalytic, template‐free hydride metal‐organic vapor phase epitaxy (solid‐vapor mechanism) and nanowires grown by a vapor‐liquid‐solid growth (VLS) mechanism in a MOVPE reactor. The nanorods and nanowires were grown on different planes of Al2O3, (0002) GaN/ Al2O3, and (001) Si. The majority of nanorods have a high structural perfection and exhibit abrupt side walls, but some of them show formation of the planar defects. Depend‐ ing on the substrate used, the size, shape and tips of the nanorods vary from hexagonal to pencil‐like. Nanowires, however have very corrugated surfaces along their side‐walls and tips, and depending on the V/III flow ratio these nanowires can have either a constant diameter or taper‐off. Their length can extend up to 100 μm. Bending and branching of nanowires was observed, but this phenomenon was never observed for nanorods. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal degradation of InGaN/GaN LEDs ohmic contacts
Authors: Meneghini M. , Trevisanello L. , Zehnder U. , Meneghesso G. , Zanoni E. 
Published: April 2008

AbstractThis paper reports an analysis of the high temperature degradation of GaN‐based LEDs. It is shown that exposure to high temperatures implies(i)the decrease of the emitted optical power,(ii)the crowding of the emission profile around the central pad and(iii)the increase of the operating voltage of the devices. Degradation is attributed to the interaction between the PECVD SiN passivation layer and the ohmic contacts at the surface of the devices: by means of the Transmission Line Method the degradation of the p‐side contacts is analyzed in detail. It is shown that high temperature treatment implies the increase of the contact resistivity of the metal/semiconductor (M/S) interface, and a slight variation of the sheet resistance of the semiconductor layer: these processes are responsible for the emission crowding and efficiency decay measured as a consequence of stress on the LEDs. Finally, it is shown that the described degradation process is reversible, after passivation removal and subsequent annealing. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature dependence of the polariton relaxation bottleneck in a GaN microcavity
Authors: Stokker‐Cheregi F. , Vinattieri A. , Colocci M. , Semond F. , Leroux M. , Massies J. , Sellers I. R. , Gurioli M. 
Published: April 2008

AbstractWe present an experimental study aimed to investigate discuss the possible presence of a phonon bottleneck in a GaN bulk microcavity. Clear anticrossing between the lower (LP) and upper polariton (UP) branches has been observed up to room temperature in photoluminescence (PL) by angular measurements with a Rabi splitting of the order of 30 meV. In order to determine the presence of a relaxation bottleneck, angular PL measurements have been performed at different temperatures for negative detuning. At low T the PL shows a clear maximum, at the angle corresponding to the resonance between the exciton and the photon modes, which is an experimental demonstration of the presence of a relaxation bottleneck. The PL enhancement in resonance condition is suppressed with increasing T and it almost disappears at room temperature. We therefore demonstrate that the exciton‐phonon interaction washes out the polariton bottleneck in GaN MCs at room temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐temperature growth of AlN in a production scale 11 × 2′ MOVPE reactor
Authors: Brunner F. , Protzmann H. , Heuken M. , Knauer A. , Weyers M. , Kneissl M. 
Published: April 2008

AbstractWe report on the growth of high quality AlN films on sapphire by MOVPE in an AIX2400G3‐HT planetary reactor. Specific reactor hardware modifications were conducted to facilitate growth temperatures of up to 1600 °C and to obtain reduced parasitic gas phase reactions. Growth was optimized regarding growth rate and surface morphology as well as optical and structural properties of the AlN layers on sapphire. With increasing growth temperature we observe a transition from an AlN surface with a high density of large pits to a smooth pit‐free morphology. The improvement in material quality with growth temperature is confirmed by X‐ray diffraction, AFM, SIMS and Raman measurements. The impact of residual or intentionally introduced Ga during growth on AlN material properties is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural features in GaN grown on a Ge(111) substrate
Authors: Zhang Y. , McAleese C. , Xiu H. , Humphreys C. J. , Lieten R. R. , Degroote S. , Borghs G. 
Published: April 2008

AbstractUsing electron microscopy, structural characterisation has been carried out on a GaN epilayer grown directly on a Ge(111) substrate using plasma assisted molecular beam epitaxy (PAMBE) without any intermediate buffer layers. It was determined that a defect with a triangular shape, initially observed with optical microscopy, is essentially a faceted void in the Ge extending from the interface into the substrate. Both hexagonal and cubic phase GaN were observed in the epilayer which may be due to temperature variation during growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The role of setback layers on the breakdown characteristics of AlGaAs/GaAs/GaN HBTs
Authors: Lian Chuanxin , Xing Huili Grace 
Published: April 2008

AbstractBreakdown voltages (VCBO) of AlGaAs/GaAs/GaAs and AlGaAs/GaAs/GaAs‐setback/GaN HBTs have been compared both theoretically and experimentally with respect to setback layer thicknesses and the doping type. VCBO was calculated using a non‐local energy model. The hard breakdown voltage was measured on as‐grown GaAs homojunctions and AlGaAs/GaAs/GaN HBTs formed by direct wafer fusion. The calculation showed an increase of VCBO from ∼ 20 V to ∼ 325 V by replacing the GaAs collector with GaN, and VCBO ∼90 V was indeed measured. The smaller than predicted VCBO is attributed to the large leakage current currently present in the fused junctions. Insertion of a lightly doped GaAs setback layer has resulted in improved current gain of the fused HBTs, but it also degrades the breakdown characteristics. 20‐30 nm setback layers were found to maintain VCBO significantly higher than that of GaAs homojunctions and likely reasonable current gains. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improvement of the surface morphology of a ‐plane InN using low‐temperature InN buffer layers
Authors: Shikata G. , Hirano S. , Inoue T. , Orihara M. , Hijikata Y. , Yaguchi H. , Yoshida S. 
Published: April 2008

AbstractWe report on the improvement of the surface morphology of a ‐plane InN films grown by RF molecular beam epitaxy. By using low‐temperature (LT) InN buffer layers, we could successfully obtain InN films with a smooth surface. The full width at half maximum values of the x‐ray diffraction (11‐20) rocking curve along the [0001] InN direction were 2870 arcsec and 3410 arcsec for a ‐plane InN samples grown at 500°C with and without LT‐InN buffer layers, respectively. Thus, we could improve also the crystalline quality of a ‐plane InN films by using LT‐InN buffer layers. We observed strong polarization anisotropy in the photoluminescence spectra of a ‐plane InN, which is typical of nonpolar wurtzite III‐nitride films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interface characterization of ALD deposited Al2O3 on GaN by CV method
Authors: Ostermaier C. , Lee H.‐C. , Hyun S.‐Y. , Ahn S.‐I. , Kim K.‐W. , Cho H.‐I. , Ha J.‐B. , Lee J.‐H. 
Published: April 2008

AbstractA high dielectric interface quality is the determining factor for high power GaN metal oxide semiconductor field‐ effect transistor (MOSFET) devices. We characterized 100 Å thick aluminum oxide (Al2O3) films deposited by ALD on MOCVD grown undoped GaN on sapphire. First we measured the leakage current and densification behaviour of the dielectric after annealing at different temperatures up to 900 °C and determined the polycrystalline phase change to be around 800 °C. Further we characterized the interface charges of both films according to the flatband shift, induced by over‐band gap UV light, showing the lowest interface charge density of 1.27 × 1011 cm–2 after thermal treatment at 850 °C. Additionally, we measured the AC conductivity and calculated the interface states density (Dit) of the upper half of the GaN bandgap, showing the lowest Dit of around 2×1010 cm–2 eV–1 at 2 eV above the valence band, while it remains higher around the band edge at 2.8×1011 cm–2 eV–1, after annealing at 750 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simple formulas for improved point‐charge electrostatics in classical force fields and hybrid quantum mechanical/molecular mechanical embedding
Authors: Cisneros G. A. , Tholander S. Na‐Im , Parisel O. , Darden T. A. , Elking D. , Perera L. , Piquemal J.‐P. 
Published: April 2008

AbstractWe present a simple damping scheme for point‐charge electrostatics that could be used directly in classical force fields. The approach acts at the charge (or monopole) level only and allows the inclusion of short‐range electrostatic penetration effects at a very low cost. Results are compared with density functional theory Coulomb intermolecular interaction energies and with several other methods such as distributed multipoles, damped distributed multipoles, and transferable Hermite‐Gaussian densities. Realistic trends in the interactions are observed for atom‐centered Mertz‐Kollman corrected point‐charge distributions. The approach allows increasing the selectivity of parameters in the case of metal complexes. In addition, two QM/MM calculations are presented where the damping function is employed to include the MM atoms located at the QM/MM boundary. The first calculation corresponds to the gas‐phase proton transfer of aspartic acid through water and the second is the first step of the reaction catalyzed by the 4‐oxalocrotonate tautomerase (4OT) enzyme. First, improved agreement is observed when using the damping approach compared with the conventional excluded charge method or when including all charges in the calculation. Second, in the case of 4OT, the damped charge approach is in agreement with previous calculations, whereas including all charges gives a significantly higher energy barrier. In both cases, no reparameterization of the van der Waals part of the force field was performed. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Molecular dynamics analysis of farnesyltransferase: A closer look into the amino acid behavior
Authors: Sousa Sérgio F. , Fernandes Pedro A. , Ramos Maria João 
Published: April 2008

AbstractFarnesyltransferase (FTase) is a zinc enzyme that catalyzes the addition of a 15 carbons isoprenoid group from farnesyl diphosphate to protein substrates containing a typical ‐CAAX motif, where C is a cysteine residue. Among the possible CAAX substrates for FTase are a large number of biologically relevant proteins involved in cancer development, including the Ras family of proteins. FTase thus quickly became a very promising target for anticancer therapy, despite the fact that a number of questions regarding its catalytic activity have remained unexplained. This study describes the successful application of three sets of molecular dynamics parameters specifically designed to allow a reliable treatment of the zinc coordination sphere in the four key intermediate states formed during the catalytic cycle of this enzyme—FTase resting state, binary complex (FTase‐FPP), ternary complex (FTase‐FPP‐CAAX), and product complex—allowing a detailed analysis of the dynamic behavior of the several amino acid residues that constitute the enzyme, and complementing the more rigid time‐averaged snapshot‐view given by the available X‐crystallographic structures with a more global structural vision that takes motion into account. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Computational optimization of AG18051 inhibitor for amyloid‐β binding alcohol dehydrogenase enzyme
Authors: Marques Alexandra T. , Antunes Agostinho , Fernandes Pedro A. , Ramos Maria J. 
Published: April 2008

AbstractAmyloid‐beta (Aβ) binding alcohol dehydrogenase (ABAD) is a multifunctional enzyme involved in maintaining the homeostasis. The enzyme can also mediate some diseases, including genetic diseases, Alzheimer's disease, and possibly some prostate cancers. Potent inhibitors of ABAD might facilitate a better clarification of the functions of the enzyme under normal and pathogenic conditions and might also be used for therapeutic intervention in disease conditions mediated by the enzyme. The AG18051 is the only presently available inhibitor of ABAD. It binds in the active‐site cavity of the enzyme and reacts with the NAD+ cofactor to form a covalent adduct. In this work, we use computational methods to perform a rational optimization of the AG18051 inhibitor, through the introduction of chemical substitutions directed to improve the affinity of the inhibitor to the enzyme. The molecular mechanics–Poisson–Boltzmann surface area methodology was used to predict the relative free binding energy of the different modified inhibitor‐NAD‐enzyme complexes. We show that it is possible to increase significantly the affinity of the inhibitor to the enzyme with small modifications, without changing the overall structure and ADME (absorption, distribution, metabolism, and excretion) properties of the original inhibitor. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Object‐oriented wrappers for the Linux kernel
Authors: Janakiram D. , Gunnam Ashok , Suneetha N. , Rajani Vineet , Reddy K. Vinay Kumar 
Published: April 2008

AbstractLinux is an open‐source operating system, which has increased in its popularity and size since its birth. Various studies have been conducted in literature on the evolution of the Linux kernel, which have shown that there are considerable maintenance problems arising out of the coupling issues in the Linux kernel and this may hamper the evolution of the kernel in future. We propose an object‐oriented (OO) wrapper‐based approach to Linux kernel to provide OO abstractions to external modules. As the major growth of the size of the Linux kernel is in device drivers, our approach provides substantial benefits in terms of developing the device drivers in C++, although the kernel is in C. Providing reusability and extensibility features to device drivers improves the maintainability of the kernel. The OO wrappers provide several benefits to module developers in terms of understandability, development ease, support for OO modules, etc. The design and implementation of C++ wrappers for Linux kernel and the performance of a device driver re‐engineered in C++ are presented in this paper. Copyright © 2008 John Wiley & Sons, Ltd.
Rheological Characteristics of Different Tropical Root Starches
Authors: Moorthy Subramony N. , Larsson Helena , Eliasson Ann‐Charlotte 
Published: April 2008

AbstractThe rheological properties of starch extracted from ten different species of tropical tuber crops were examined using a Bohlin rheometer. Suspensions with starch concentrations of 3, 4 and 5% were gelatinised at 75°C and fed into the rheometer cup. A C 25 measuring system was used and the heating rate was 1.5°C/min, heating schedule 75‐95ºC, holding at 95°C for 600 s, cooling to 35°C at 1.5ºC/min, holding for 3600 s. For strain sweep tests, the range of strain used was 0‐0.2% and the temperature of test was 35ºC. The data on viscosity, storage modulus (G′) and phase angle were obtained from the rheograms. The results indicated variability in the various properties of the different starches. However the results did not follow a definite trend. The viscosity of Colocasia starch was low while Canna edulis and yam starches had high viscosities. The storage modulus was also highest for Canna starch (70‐93 Pa) for 5% and gel strength was comparatively high for Canna edulis, Dioscorea esculenta and D. rotundata starches. The phase angle values followed the pattern of G′ and all the starch pastes were found to be elastic in nature at higher concentration. The wide variability in rheological properties can be useful in different applications of tuber starches.
Application of an unsupervised artificial neural network technique to multivariant surface water quality data
Authors: Çinar Özer , Merdun Hasan 
Published: April 2008

AbstractSurface water contamination from agricultural and urban runoff and wastewater discharges from industrial and municipal activities is of major concern to people worldwide. Classical models can be insufficient to visualise the results because the water quality variables used to describe dynamic pollution sources are complex, multivariable, and nonlinearly related. Artificial intelligence techniques with the ability to analyse multivariant water quality data by means of a sophisticated visualisation capacity can offer an alternative to current models. In this study, the Kohonen self‐organising feature maps (SOM) neural network was initially applied to analyse the complex nonlinear relationships among multivariable surface water quality variables using the component planes of the variables to determine the complex behaviour of water quality parameters. The dependencies between water quality variables were extracted and interpreted using the pattern analysis visualised in component planes. For further investigation, the k‐means clustering algorithm was used to determine the optimal number of clusters by partitioning the maps and utilising the Davies–Bouldin clustering index, leading to seven groups or clusters corresponding to water quality variables. The results reveal that the concentrations of Na, K, Cl, NH4‐N, NO2‐N, o‐PO4, component planes of organic matter (pV), and dissolved oxygen (DO) were significantly affected by seasonal changes, and that the SOM technique is an efficient tool with which to analyse and determine the complex behaviour of multidimensional surface water quality data. These results suggest that this technique could also be applied to other environmentally sensitive areas such as air and groundwater pollution.