A systematic approach for improving the quality of official statistics: Case of Korean information and telecommunication industry

With the rapid growth of information and communication technology (ICT) in Korea, there was a need to improve the quality of official ICT statistics. In order to do this, various factors had to be considered, such as the quality of surveying, processing, and output as well as the reputation of the statistical agency. We used PLS estimation to determine how these factors might influence customer satisfaction. Furthermore, through a comparison of associated satisfaction indices, we provided feedback to the responsible statistics agency. It appears that our model can be used as a tool for improving the quality of official ICT statistics. © 2008 Elsevier B.V. All rights reserved.

An efficient approach of modelling the flexural cracking behaviour of un-notched plain concrete prisms subject to monotonic and cyclic loading

In the field of vibration-based damage detection of concrete structures efficient damage models are needed to better understand changes in the vibration properties of cracked structures. These models should quantitatively replicate the damage mechanisms in concrete and easily be used as damage detection tools. In this paper, the flexural cracking behaviour of plain concrete prisms subject to monotonic and cyclic loading regimes under displacement control is tested experimentally and modelled numerically. Four-point bending tests on simply supported un-notched prisms are conducted, where the cracking process is monitored using a digital image correlation system. A numerical model, with a single crack at midspan, is presented where the cracked zone is modelled using the fictitious crack approach and parts outside that zone are treated in a linear-elastic manner. The model considers crack initiation, growth and closure by adopting cyclic constitutive laws. A multi-variate Newton-Raphson iterative solver is used to solve the non-linear equations to ensure equilibrium and compatibility at the interface of the cracked zone. The numerical results agree well with the experiments for both loading scenarios. The model shows good predictions of the degradation of stiffness with increasing load. It also approximates the crack-mouth-opening-displacement when compared with the experimental data of the digital image correlation system. The model is found to be computationally efficient as it runs full analysis for cyclic loading in less than 2. min, and it can therefore be used within the damage detection process. © 2013 Elsevier Ltd.

A novel theoretical approach to passive control of thermo-acoustic oscillations: Application to ducted heat sources

In this paper, we develop a linear technique that predicts how the stability of a thermo-acoustic system changes due to the action of a generic passive feedback device or a generic change in the base state. From this, one can calculate the passive device or base state change that most stabilizes the system. This theoretical framework, based on adjoint equations, is applied to two types of Rijke tube. The first contains an electrically-heated hot wire and the second contains a diffusion flame. Both heat sources are assumed to be compact so that the acoustic and heat release models can be decoupled. We find that the most effective passive control device is an adiabatic mesh placed at the downstream end of the Rijke tube. We also investigate the effects of a second hot wire and a local variation of the cross-sectional area but find that both affect the frequency more than the growth rate. This application of adjoint sensitivity analysis opens up new possibilities for the passive control of thermo-acoustic oscillations. For example, the influence of base state changes can be combined with other constraints, such as that the total heat release rate remains constant, in order to show how an unstable thermo-acoustic system should be changed in order to make it stable. Copyright © 2013 by ASME.

Increased carbon nanotube area density after catalyst generation from cobalt disilicide using a cyclic reactive ion etching approach

We used a cyclic reactive ion etching (RIE) process to increase the Co catalyst density on a cobalt disilicide (CoSi2) substrate for carbon nanotube (CNT) growth. Each cycle of catalyst formation consists of a room temperature RIE step and an annealing step at 450 °C. The RIE step transfers the top-surface of CoSi2 into cobalt fluoride; while the annealing reduces the fluoride into metallic Co nanoparticles. We have optimized this cyclic RIE process and determined that the catalyst density can be doubled in three cycles, resulting in a final CNT shell density of 6.6 × 10 11 walls·cm-2. This work demonstrates a very effective approach to increase the CNT density grown directly on silicides. © 2014 AIP Publishing LLC.

High performance transistors based on the controlled growth of triisopropylsilylethynyl-pentacene crystals via non-isotropic solvent evaporation

Triisopropylsilylethynyl-pentacene (TIPS-PEN) has proven to be one of the most promising small molecules in the field of molecular electronics, due to its unique features in terms of stability, performance and ease of processing. Among a wide variety of well-established techniques for the deposition of TIPS-PEN, blade-metered methods have recently gained great interest towards the formation of uniform crystalline films over a large area. Following this rationale, we herein designed a versatile approach based on blade-coating, which overcomes the problem of anisotropic crystal formation by manipulating the solvent evaporation behaviour, in a way that brings about a preferential degree of crystal orientation. The applicability of this method was evaluated by fabricating field-effect transistors on glass as well as on silicon dioxide/silicon (SiO2/Si) substrates. Interestingly, in an attempt to improve the rheological and wetting behaviour of the liquid films on the SiO2/Si substrates, we introduced a polymeric interlayer of polystyrene (PS) or polymethylmethacrylate (PMMA) which concurrently acts as passivation and crystallization assisting layer. In this case, the synergistic effects of the highly-ordered crystalline structure and the oxide surface modification were thoroughly investigated. The overall performance of the fabricated devices revealed excellent electrical characteristics, with high saturation mobilities up to 0.72 cm2 V-1 s-1 (on glass with polymeric dielectric), on/off current ratio >104 and low threshold voltage values (<-5 V). This journal is © the Partner Organisations 2014.

Study of GaN growth on ultra-thin Si membranes

10 mu m-thick ultra-thin Si (111) membranes for GaN epi-layers growth were successfully fabricated on silicon-on-insulator (SOI) substrate by backside etching the handle Si and buried oxide (BOX) layer. Then 1 mu m-thick GaN layers were deposited on these Si membranes by metal-organic chemical vapor deposition (MOCVD). The crack-free areas of 250 mu m, x 250 mu m were obtained on the GaN layers due to the reduction of thermal stress by using these ultra-thin Si membranes, which was further confirmed by the photoluminescence (PL) spectra and the simulation results from the finite element method calculation by using the software of ANSYS. In this paper, a newly developed approach was demonstrated to utilize micromechanical structures for GaN growth, which would improve the material quality of the epi-layers and facilitate GaN-based micro electro-mechanical system (MEMS) fabrication, especially the pressure sensor, in the future applications. (C) 2008 Elsevier Ltd. All rights reserved.

The compact microcrystalline Si thin film with structure uniformity in the growth direction by hydrogen dilution profile

The hydrogen dilution profiling (HDP) technique has been developed to improve the quality and the crystalline uniformity in the growth direction of mu c-Si:H thin films prepared by hot-wire chemical-vapor deposition. The high H dilution in the initial growth stage reduces the amorphous transition layer from 30-50 to less than 10 nm. The uniformity of crystalline content X-c in the growth direction was much improved by the proper design of hydrogen dilution profiling which effectively controls the nonuniform transition region of Xc from 300 to less than 30 nm. Furthermore, the HDP approach restrains the formation of microvoids in mu c-Si: H thin films with a high Xc and enhances the compactness of the film. As a result the stability of mu c-Si: H thin films by HDP against the oxygen diffusion, as well as the electrical property, is much improved. (c) 2005 American Institute of Physics.

A 10-GHz bandwidth electroabsorption modulated laser by ultra-low-pressure selective area growth

A novel integration technique has been developed using band-gap energy control of InGaAsP/InGaAsP multi-quantum-well (MQW) structures during simultaneous ultra-low-pressure (22 mbar) selective-area-growth (SAG) process in metal-organic chemical vapour deposition. A fundamental study of the controllability of band gap energy by the SAG method is performed. A large band-gap photoluminescence wavelength shift of 83nm is obtained with a small mask width variation (0-30 mu m). The method is then applied to fabricate an MQW distributed-feedback laser monolithically integrated with an electroabsorption modulator. The experimental results exhibit superior device characteristics with low threshold of 19 mA, over 24 dB extinction ratio when coupled into a single mode fibre. More than 10GHz modulation bandwidth is also achieved, which demonstrates that the ultra-low-pressure SAG technique is a promising approach for high-speed transmission photonic integrated circuits.

Substrate surface atomic structure influence on the growth of InAlAs quantum dots

We have examined the influence of substrate surface orientation on self-assembled InAlAs/AlGaAs quantum dots grown on (0 0 1) and (n 1 1) A/B (n = 3, 5) GaAs substrates by molecular beam epitaxy (MBE). Preliminary characterizations have been performed using photoluminescence (PL) and transmission electron microscopy (TEM). The PL emission energies of quantum dots on high Miller index surface are found to be strongly dependent on the atomic-terminated surface (A or B surface) of the substrate. We observed that there were planar ordering larger islands on (3 1 1)B surface compared to (0 0 1) surface, in contrast, a rough interface and smaller "grains" on (3 1 1)A surface, this result is identical with PL emission energy from these islands. We propose that the rapid strain-induced surface "roughening" impedes the formation of 3D islands on A surface, and indicating that this is a promising approach of the realization of ordering distribution on (3 1 1)B plane for devices such as red-emitting semiconductor quantum dots lasers. (C) 1999 Elsevier Science B.V. All rights reserved.

Self-limiting MBE growth and characterization of three-dimensionally confined nanostructures on patterned GaAs(311)A substrates

The formation of triangular-shaped dot-like (TD) structures grown by molecular beam epitaxy on GaAs (311)A substrates patterned with square- and triangular-shaped holes is compared. On substrates patterned with square-shaped holes, TD structures are formed via the pinch-off of two symmetrically arranged {111} planes which develop freely in the regions between the holes on the original substrate surface, while the (111)A sidewalls of the as-etched holes develop a rough morphology during growth. The evolution of the rough ( 1 1 1)A sidewalls is eliminated on substrates patterned with triangular shaped holes resulting in similar TD structures with highly improved uniformity over the entire pattern. Spectrally and spatially resolved cathodoluminescence spectroscopy reveals the lateral variation of the quantum-well confinement energy in the TD structures generating distinct lateral energy barriers between the top portion and the nearby smooth regions with efficient radiative recombination. Formation of TD structures provides a new approach Do fabricate three-dimensionally confined nanostructures in a controlled manner.

Molecular-beam epitaxial growth of position controlled InAs islands on cleaved edge of InGaAs/GaAs superlattice

A promising approach for positioning of InAs islands on (110)GaAs is demonstrated. By combining self-assembly of quantum dots with solid source molecular beam epitaxy (MBE) on cleaved edge of InGaAs/GaAs superlattice (SL), linear alignment of InAs islands on the InGaAs strain layers have been fabricated The cleaved edge of InGaAs/GaAs SL acts as strain nanopattern for InAs selective growth. Indium atoms incident on the surface will preferentially migrate to InGaAs regions where favorable bonding sites are available. The strain nanopattern's effect is studied by the different indium fraction and thickness of InxGa1-xAs/GaAs SL. The ordering of the InAs islands is found to depend on the properties of the underlying InGaAs strain layers.

Diamond growth by carbon ion implantation of diamond

Medium energy (5-25 keV) C-13(+) ion implantation into diamond (100) to a fluence ranging from 10(16) cm(-2) to 10(18) cm(-2) was performed for the study of diamond growth via the approach of ion beam implantation. The samples were characterized with Rutherford backscattering/channelling spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and Auger electron spectroscopy. Extended defects are formed in the cascade collision volume during bombardment at high temperatures. Carbon incorporation indeed induces a volume growth but the diamond (100) samples receiving a fluence of 4 x 10(17) to 2 x 10(18) at. cm(-2) (with a dose rate of 5 x 10(15) at. cm(-2) s(-1) at 5 to 25 keV and 800 degrees C) showed no He-ion channelling. Common to these samples is that the top surface layer of a few nanometers has a substantial amount of graphite which can be removed by chemical etching. The rest of the grown layer is polycrystalline diamond with a very high density of extended defects.

A 10-GHz Bandwidth Electroabsorption Modulated Laser by Ultra-Low-Pressure Selective Area Growth

A novel integration technique has been developed using band-gap energy control of InGaAsP/InGaAsP multiquantum-well (MQW) structures during simultaneous ultra-low-pressure (22 mbar) selective-area-growth (SAG) process in metal-organic chemical vapour deposition. A fundamental study of the controllability of band gap energy by the SAG method is performed. A large band-gap photoluminescence wavelength shift of 83nm is obtained with a small mask width variation (0-30μm). The method is then applied to fabricate an MQW distributed-feedback laser monolithically integrated with an electroabsorption modulator. The experimental results exhibit superior device characteristics with low threshold of 19mA, over 24 dB extinction ratio when coupled into a single mode fibre. More than 10 GHz modulation bandwidth is also achieved, which demonstrates that the ultra-low-pressure SAG technique is a promising approach for high-speed transmission photonic integrated circuits.

Climate change, sea level rise and integrated coastal zone management: An IPCC approach

Expansion of economic activities, urbanisation, increased resource use and population growth are continuously increasing the vulnerability of the coastal zone. This vulnerability is now further raised by the threat of climate change and accelerated sea level rise. The potentially severe impacts force policy-makers to also consider long-term planning for climate change and sea level rise. For reasons of efficiency and effectiveness this long-term planning should be integrated with existing short-term plans, thus creating an Integrated Coastal Zone Management programme. As a starting point for coastal zone management, the assessment of a country's or region's vulnerability to accelerated sea level rise is of utmost importance. The Intergovernmental Panel on Climate Change has developed a common methodology for this purpose. Studies carried out according to this Common Methodology have been compared and combined, from which general conclusions on local, regional and global vulnerability have been drawn, the latter in the form of a Global Vulnerability Assessment. In order to address the challenge of coping with climate change and accelerated sea level rise, it is essential to foresee the possible impacts, and to take precautionary action. Because of the long lead times needed for creating the required technical and institutional infrastructures, such action should be taken in the short term. Furthermore, it should be part of a broader coastal zone management and planning context. This will require a holistic view, shared by the different institutional levels that exist, along which different needs and interests should be balanced.

Syntheses of opened hollow clay microspheres through a spray-drying approach and their derivative clay/carbon nanotubes composites

Opened hollow microspheres of organoclays were prepared via spray drying the suspension of modified Na+-montmorillonite (Na+-MMT) with alkylsulfonate. The microstructure and thermal properties of these opened hollow spheres were characterized by means of wide-angle X-ray diffraction, field emission scanning electron microscopy, and thermogravimetric analysis. The results showed that the organoclays had larger interlayer spacing compared with pure Na+-MMT and higher thermal stability relative to the alkylsufonate.