bluuebunny/crossref_metadata_2025_split huggingface dataset:
Smoothed aggregation solvers for anisotropic diffusion
Authors: Schroder Jacob B. 
Published: January 2012

SUMMARYA smoothed aggregation‐based algebraic multigrid solver for anisotropic diffusion problems is presented. Algebraic multigrid is a popular and effective method for solving sparse linear systems that arise from discretizing partial differential equations. However, although algebraic multigrid was designed for elliptic problems, the case of non‐grid‐aligned anisotropic diffusion is not adequately addressed by existing methods. To achieve scalable performance, it is shown that neither new coarsening nor new relaxation strategies are necessary. Instead, a novel smoothed aggregation approach is developed that combines long‐distance interpolation, coarse‐grid injection, and an energy‐minimization strategy that finds the interpolation weights. Previously developed theory by Falgout and Vassilevski is used to discern that existing coarsening strategies are sufficient, but that existing interpolation methods are not. In particular, an interpolation quality measure tracks ‘closeness’ to the ideal interpolant and guides the interpolation sparsity pattern choice. Although the interpolation quality measure is computable for only small model problems, an inexact, but computable, measure is proposed for larger problems. This paper concludes with encouraging numerical results that also potentially show broad applicability (e.g., for linear elasticity). Copyright © 2012 John Wiley & Sons, Ltd.
On condition numbers for Moore–Penrose inverse and linear least squares problem involving Kronecker products
Authors: Diao Huaian , Wang Weiguo , Wei Yimin , Qiao Sanzheng 
Published: January 2012

SUMMARYIn this paper, we investigate the normwise, mixed, and componentwise condition numbers and their upper bounds for the Moore–Penrose inverse of the Kronecker product and more general matrix function compositions involving Kronecker products. We also present the condition numbers and their upper bounds for the associated Kronecker product linear least squares solution with full column rank. In practice, the derived upper bounds for the mixed and componentwise condition numbers for Kronecker product linear least squares solution can be efficiently estimated using the Hager–Higham Algorithm. Copyright © 2012 John Wiley & Sons, Ltd.
Effective surface passivation of AlGaN/GaN heterostructures by using PH3 plasma treatment and HfO2 dielectric
Authors: Zhang Chunfu , Hao Yue , Feng Qian 
Published: January 2012

AbstractDifferent surface passivation methods of AlGaN/GaN heterostructures were investigated in this work. C‐V measurement shows that very high trap density (Dit) of 1.51×1013cm‐2eV‐1 exists at the AlGaN/GaN surface, which has activation energy of 0.765 eV. The surface treatment by using O2 plasma treatment and HfO2 dielectric can efficiently lower Dit to 3.57×1012cm‐2eV‐1 and 1.06×1012cm‐2eV‐1, repectively. To reduce these deep trap states further, a more effective passivation method is presented here. By using the PH3 plasma treatment before the HfO2 deposition, Dit was further greatly reduced and reached a very low value of 1.37×1011cm‐2eV‐1. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relationship between residual carrier density and phase purity in InN grown by pressurized‐reactor MOVPE
Authors: Prasertsuk Kiattiwut , Hirata Masaki , Liu Yuhuai , Kimura Takeshi , Zhang Yuantao , Iwabuchi Takuya , Katayama Ryuji , Matsuoka Takashi 
Published: January 2012

AbstractWe have studied the relationship between the residual carrier density and the phase purity of the InN films grown on α‐Al2O3 substrate by pressurized‐reactor metalorganic vapour phase epitaxy. As simple and non‐destructive measurement methods of carrier density (ne), the plasmon dispersion analysis by the IR reflection spectra, and the estimation by the absorption edge of the IR transmission spectra have been adopted for the epitaxial InN films at room temperature, using Fourier transform infrared (FT‐IR) spectrometer. With increasing the growth temperature, plasma frequency estimated from the reflectance analysis shifts to the lower frequency which means the decrease of ne associated with the improvement of the crystal quality. Especially in case of zincblende containing InN grown at low temperature, the discrepancy occurred between ne derived from two methods. The ne analyzed in terms of the electronic band filling effect was found to be underestimated due to the use of bandgap energy of wurtzite phase instead of zincblende, since the bandgap energy of the latter has been reported to be 0.48 eV, much smaller than that of wurtzite, 0.68 eV. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sequential tunneling transport in GaN/AlGaN quantum cascade structures
Authors: Sudradjat Faisal F. , Zhang Wei , Driscoll Kristina , Liao Yitao , Bhattacharyya Anirban , Thomidis Christos , Zhou Lin , Smith David J. , Moustakas Theodore D. , Paiella Roberto 
Published: January 2012

AbstractWe demonstrate electronic sequential tunneling transport through the ground‐state subbands of GaN/Al0.15Ga0.85N quantum cascade structures grown on free‐standing GaN substrates. A pronounced transition from a high‐ to a low‐resistance state is observed as the applied voltage is increased. The measured current‐voltage characteristics are found to vary with temperature, structure design, and polarity of the applied bias, in a way that is fully consistent with theoretical expectations. The dominant transport mechanism is determined to be scattering‐assisted tunneling. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Highly enhanced migration in Pt‐catalyst‐assisted MOVPE InN by controlling the catalyst temperature
Authors: Sugita K. , Hotta T. , Hironaga D. , Mihara A. , Bhuiyan A. G. , Hashimoto A. , Yamamoto A. 
Published: January 2012

AbstractThis paper reports on the catalyst‐assisted metal‐organic vapor phase epitaxy (CA‐MOVPE) growth of InN with an independent control of catalyst temperature. When the catalyst temperature is increased above the growth temperature of InN, the grain size becomes large and full width at half maximum (FWHM) of X‐ray rocking curve (XRC) is drastically decreased The migration of precursors is highly enhanced and the crystal quality is improved by CA‐MOVPE with an independent heating system of the catalyst. This CA‐MOVPE system will open the possibility of the growth of high‐quality InN and In containing alloys especially with the higher In content (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improved crystalline quality and light output power of GaN‐based light‐emitting diodes grown on Si substrate by buffer optimization
Authors: Zou Xinbo , Wong Ka Ming , Yu Naisen , Chen Peng , Lau Kei May 
Published: January 2012

AbstractHigh‐quality crack‐free GaN‐based light‐emitting diodes (LEDs) were grown on patterned Si substrate using a flow modulation method and a high‐temperature (HT)‐AlN/AlGaN superlattice structure (SLs) interlayer. The effects of these two techniques on material properties and device performance were studied. The enhanced crystalline quality can be attributed to a 3D to 2D coalescence process with fewer dislocations initiated from the interlayers. The light output power of blue LEDs was improved by 66% after successful implementation of flow modulation and new interlayers. After substrate removal and packaging, the optical power of circle LEDs with diameter of 300 μm could reach as high as 6.30 mW at 20 mA. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐efficiency AlGaN deep‐UV LEDs fabricated on a‐ and m‐axis oriented c‐plane sapphire substrates
Authors: Fujikawa Sachie , Hirayama Hideki , Maeda Noritoshi 
Published: January 2012

AbstractWe demonstrated high‐efficiency 270 nm‐band AlGaN deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) fabricated on 0.15° off a‐ and m‐axis oriented c‐plane (0001) sapphire substrates grown by low‐pressure metal organic chemical‐vapor deposition (LP‐MOCVD). An approximately 4.5 μm‐thick low threading dislocation density (TDD) AlN template was grown on the sapphire substrate by using an NH3 pulsed‐flow multilayer (ML) growth method. We found that atomically flat surface can be easily obtained for AlN layer grown on a‐axis oriented sample. On the other hand, a step‐bunching was observed for the surface of AlN layer grown on m‐axis oriented sample. We found, from these results, that a‐axis oriented (0001) sapphire is more suitable for obtaining a flat surface in AlN template without step‐bunching. We also found that shorter wavelength LED can be obtained by using an a‐axis oriented (0001) sapphire, because an Al incorporation in AlGaN is slightly high for the growth on a‐axis oriented (0001) sapphire. We achieved high‐efficiency AlGaN quantum well (QW) DUV LEDs on AlN templates grown on both a‐ and m‐axis oriented sapphire substrates. The peak wavelengths of the LEDs fabricated on a‐ and m‐axis oriented sapphire were 270 and 277 nm, respectively. The maximum external quantum efficiencies (EQEs) of the LEDs fabricated on a‐ and m‐axis oriented sapphire were 3.8 and 3.2%, respectively, measured under room temperature (RT) continuous wave (CW) operations. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Studies of efficiency droop in GaN based LEDs
Authors: Phillips W. A. , Thrush E. J. , Zhang Y. , Humphreys C. J. 
Published: January 2012

AbstractEL measurements have been made on a number of commercial LEDs as a function of drive current density “J” and temperature “T”. For one type of LED, (sample A), the magnitude of the peak in quantum efficiency (QE) is almost independent of temperature and the QE as a function of J can be successfully modelled in terms of the well‐known J=An+Bn2+Cn3 expression using the same relative magnitudes of B and C at different temperatures, with A alone increasing with increasing temperature. In another type, the peak in QE occurs at values of J that decrease with decreasing temperature but in this sample there is evidence of quantum well inhomogeneity. The weak temperature dependence of the C coefficient in sample A is strong evidence against thermally activated current leakage, mid‐gap trapping centres or intra‐band Auger recombination being dominant mechanisms for droop. The EL spectra show strong phonon replicas at low temperatures, but a lineshape analysis allows the main emission linewidth to be derived as a function of J and T. A model based on inhomogeneous broadening provides a good explanation for the results, and provides a link between the value of B and the effective 2D density of states. The results suggest that the most likely mechanism for droop in these devices is an indirect Auger effect mediated by phonons or localised states (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of 100 nm gate AlGaN/GaN HEMT and MMIC technology suitable for mm‐wave applications
Authors: Brückner Peter , Kiefer R. , Haupt C. , Leuther A. , Müller S. , Quay R. , Schwantuschke D. , Mikulla M. , Ambacher O. 
Published: January 2012

AbstractIn this paper a Gallium Nitride MMIC technology for RF‐ and microwave and high power amplifiers based on 100 nm gate technology is presented. The MMIC technology includes alloyed ohmic contacts, T‐shaped 100 nm gates, air‐bridges, MIM capacitors, inductors, and a full through wafer viahole backside process. As a key element for a high MMIC yield, we'll present low ohmic contact resistances with a high yield on several wafers in different processing batches and low leakage currents for a reliable device performance, respectively. Single HEMT performance exhibits PAE values of up to 60% and power densities of 1.3 W/mm. For a single stage power amplifier with a WG = 4 × 45 µm dual‐gate HEMT configuration, a gain beyond 10 dB at 60 GHz is presented. By using only one transistor for the amplifier stage, a maximum output power of more than 21 dBm and a PAE of 9.3% is achieved. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigations on Si‐doped AlGaN: Below and above the Mott density
Authors: Forghani Kamran , Gharavipour Mohammadreza , Scholz Ferdinand , Thonke Klaus 
Published: January 2012

AbstractSi doped AlxGa1‐xN layers with x ranging from 0 to 45% have been grown by metal‐organic vapour phase epitaxy in order to study their electrical properties. The Si doping concentration was varied over a wide range below and above the theoretically expected Mott density. By per­forming variable temperature Hall‐effect measurements on such epilayers, we could evaluate the donor ionization energy as a function of the Al content x and the Si doping concentration. As expected, we observed a very low ionization energy for Si concentrations above the Mott density (for which the conductivity changes towards metallic conductivity). The evaluated ionization energies for low carrier concentrations fit well with the predicted Si ionization energies (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Distribution of built‐in electric field in GaN(cap)/AlGaN/GaN(buffer) transistor heterostructures with various AlGaN thicknesses
Authors: Gladysiewicz M. , Kudrawiec R. 
Published: January 2012

AbstractA theoretical approach supported by experimental data (i.e., measurements of built‐in electric field in AlGaN layer and two dimensional electron gas (2DEG) concentration at the AlGaN/GaN interface) has been proposed to determine the distribution of built‐in electric field in undoped polar GaN(cap)/AlGaN/GaN(buffer) heterostructures. In this method the Schrodinger and Poisson equations are solving self consistently for various boundary conditions. It is clearly shown that the built‐in electric field in AlGaN layer depends mainly on the surface boundary condition whereas the concentration of 2DEG at AlGaN/GaN interface depends on two boundary conditions (i.e., the Fermi‐level position on GaN(cap) surface and inside GaN(buffer) layer). Comparing the measured built‐in electric field in AlGaN layer with this one calculated for various Fermi‐level position on GaN surface it is possible to determine the Fermi‐level pinning on GaN(cap) surface. Next it is possible to determine the Fermi‐level position in GaN(buffer) layer at a given distance from AlGaN/GaN interface. For this purpose the measured 2DEG concentration was compared with this one calculated for the fixed Fermi‐level position on GaN(cap) surface and the varied Fermi‐level position in GaN buffer layer. In this way the distribution of built‐in electric can be determined for real heterostructures for which the built‐in electric field in AlGaN layer is measured by electromodulation spectroscopy and 2DEG concentration is extracted from Hall measurements. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron holography of an in‐situ biased GaN‐based LED
Authors: Liu L. Z.‐Y. , McAleese C. , Sridhara Rao D. V. , Kappers M. J. , Humphreys C. J. 
Published: January 2012

AbstractElectron holography was used to measure the electrostatic potential distribution in an LED chip at high spatial resolution, from which the internal polarization field can be derived. A cross‐sectional TEM lamella on a workable LED die containing five InGaN/GaN quantum wells (QWs) connected to electrodes that fit into an in‐situ biasing TEM holder was prepared using a focused ion beam (FIB). Off‐axis electron holography under Lorentz mode was carried out to study the p ‐MQW‐n region and phase profiles were derived at different reverse biasing conditions. p ‐n contrast has been shown in the calibrated electrostatic potential mapping. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of GaN and AlGaN on (100) β‐Ga2O3 substrates
Authors: Ito Shun , Takeda Kenichiro , Nagata Kengo , Aoshima Hiroki , Takehara Kosuke , Iwaya Motoaki , Takeuchi Tetsuya , Kamiyama Satoshi , Akasaki Isamu , Amano Hiroshi 
Published: January 2012

AbstractThe crystalline quality of GaN and Al0.08Ga0.92N epitaxial layers on (100) β‐Ga2O3 substrates was significantly improved by the facet‐controlled growth method. The facets were controlled by changing the nitrogen ambient thermal annealing temperature. We demonstrated the high‐crystalline‐quality GaN and Al0.08Ga0.92N on β‐Ga2O3 substrates, which were comparable to GaN and AlGaN on sapphire substrates using low‐temperature buffer layers. This method is useful for the fabrication of vertical‐type ultraviolet (UV) light‐emitting diodes (LEDs) on β‐Ga2O3 substrates. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of InGaN/GaN epitaxial layers by aberration corrected TEM/STEM
Authors: Amari Houari , Ross Ian M. , Wang Tao , Walther Thomas 
Published: January 2012

AbstractIn this study, the thickness, interface quality, and elemental composition of InGaN/GaN epitaxial layers are investigated. Samples were grown by Metal‐Organic Chemical Vapour Deposition (MOCVD) on sapphire (0001) substrates. The structure was designed to form In0.1Ga0.9N quantum wells (QWs) with thicknesses decreasing from 8 nm to 0.25 nm embedded between 10 nm GaN barriers. Scanning transmission electron microscopy (S)TEM, energy‐dispersive X‐ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS) have been applied using both a JEOL 2010F field‐emission gun (FEG) TEM/STEM microscope and the newly developed spherical aberration‐corrected JEOL R005 cold FEG (S)TEM. The peak indium concentration of the widest QWs was determined to lie between 0.12 and 0.15 (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and stacking fault reduction in semi‐polar GaN films on planar Si(112) and Si(113)
Authors: Ravash Roghaiyeh , Veit Peter , Müller Mathias , Schmidt Gordon , Dempewolf Anja , Hempel Thomas , Bläsing Jürgen , Bertram Frank , Dadgar Armin , Christen Jürgen , Krost Alois 
Published: January 2012

AbstractWe report on metal organic vapor phase epitaxy of semi‐polar growth of nearly (1$ \bar 1 $06) oriented GaN films on Si(112) and (1$ \bar 1 $05) and (1$ \bar 1 $04) GaN on Si(113). We analyze the GaN crystallites by field emission‐scanning electron microscopy (FE‐SEM), scanning transmission electron microscopy (STEM), photoluminescence (PL), and cathodoluminescence (CL). A correlation between optical properties and microstructure is presented. Our studies reveal a significant reduction of basal plane stacking faults (BSFs) in semi‐polar GaN grown on planar Si(112) by applying a low temperature (LT) AlN interlayer. We find that the insertion of the LT‐AlN interlayer can eliminate the stacking faults in the upper GaN layer, when the LT‐AlN interlayer is inserted on a smooth GaN buffer. The LT‐AlN interlayer results in lattice relaxation due to misfit dislocation formation at the GaN/LT–AlN interface. In comparison, GaN grown on Si(113) with same growth conditions and a rough GaN surface does not show any BSF reduction while it is reduced for a smooth GaN layer (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Allergen Arrays for Antibody Screening and Immune Cell Activation Profiling Generated by Parallel Lipid Dip‐Pen Nanolithography
Authors: Sekula‐Neuner Sylwia , Maier Jana , Oppong Emmanuel , Cato Andrew C. B. , Hirtz Michael , Fuchs Harald 
Published: January 2012

AbstractMultiple‐allergen testing for high throughput and high sensitivity requires the development of miniaturized immunoassays that allow for a large test area and require only a small volume of the test analyte, which is often available only in limited amounts. Developing such miniaturized biochips containing arrays of test allergens needs application of a technique able to deposit molecules at high resolution and speed while preserving its functionality. Lipid dip‐pen nanolithography (L‐DPN) is an ideal technique to create such biologically active surfaces, and it has already been successfully applied for the direct, nanoscale deposition of functional proteins, as well as for the fabrication of biochemical templates for selective adsorption. The work presented here shows the application of L‐DPN for the generation of arrays of the ligand 2,4‐dinitrophenyl[1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphoethanolamine‐N‐[6‐[(2,4‐dinitrophenyl)amino]hexanoyl] (DNP)] onto glass surfaces as a model system for detection of allergen‐specific Immunoglobin E (IgE) antibodies and for mast cell activation profiling.
Structural insight into RNA recognition motifs: versatile molecular Lego building blocks for biological systems
Authors: Muto Yutaka , Yokoyama Shigeyuki 
Published: January 2012

Abstract‘RNA recognition motifs (RRMs)’ are common domain‐folds composed of 80–90 amino‐acid residues in eukaryotes, and have been identified in many cellular proteins. At first they were known as RNA binding domains. Through discoveries over the past 20 years, however, the RRMs have been shown to exhibit versatile molecular recognition activities and to behave as molecular Lego building blocks to construct biological systems. Novel RNA/protein recognition modes by RRMs are being identified, and more information about the molecular recognition by RRMs is becoming available. These RNA/protein recognition modes are strongly correlated with their biological significance. In this review, we would like to survey the recent progress on these versatile molecular recognition modules. WIREs RNA 2012, 3:229–246. doi: 10.1002/wrna.1107This article is categorized under:

RNA Interactions with Proteins and Other Molecules > Protein–RNA Recognition
RNA Interactions with Proteins and Other Molecules > RNA–Protein Complexes
Risky Business: Risk Perception and the Use of Medical Services among Customers of DTC Personal Genetic Testing
Authors: Kaufman David J. , Bollinger Juli M. , Dvoskin Rachel L. , Scott Joan A. 
Published: January 2012

AbstractDirect‐to‐consumer genetic testing has generated speculation about how customers will interpret results and how these interpretations will influence healthcare use and behavior; however, few empirical data on these topics exist. We conducted an online survey of DTC customers of 23andMe, deCODEme, and Navigenics to begin to address these questions. Random samples of U.S. DTC customers were invited to participate. Survey topics included demographics, perceptions of two sample DTC results, and health behaviors following DTC testing. Of 3,167 DTC customers invited, 33% (n = 1,048) completed the survey. Forty‐three percent of respondents had sought additional information about a health condition tested; 28% had discussed their results with a healthcare professional; and 9% had followed up with additional lab tests. Sixteen percent of respondents had changed a medication or supplement regimen, and one‐third said they were being more careful about their diet. Many of these health‐related behaviors were significantly associated with responses to a question that asked how participants would perceive their colon cancer risk (as low, moderate, or high) if they received a test result showing an 11% lifetime risk, as compared to 5% risk in the general population. Respondents who would consider themselves to be at high risk for colon cancer were significantly more likely to have sought information about a disease (p = 0.03), discussed results with a physician (p = 0.05), changed their diet (p = 0.02), and started exercising more (p = 0.01). Participants’ personal health contexts—including personal and family history of disease and quality of self‐perceived health—were also associated with health‐related behaviors after testing. Subjective interpretations of genetic risk data and personal context appear to be related to health behaviors among DTC customers. Sharing DTC test results with healthcare professionals may add perceived utility to the tests.