Numerical analysis for transient point defect behavior in Czochralski silicon crystal growth

To study the transient point defect distribution in Czochralski-grown silicon single crystals, a continuum model of point defect dynamics to predict the concentration of interstitial and vacancy is established by estimating expressions for the thermo-physical properties of point defects and the point defect distribution in silicon crystals. It is well known that the concentration of intrinsic point defects in growing silicon crystals is a function of the crystal pull rate (V) and the temperature gradient (G) at the solidification interface inside the crystal, and steady state predictions from point defect dynamics are well agreed with experiment. In this study, finite element simulations have been performed for the growth halt experiment with 150 mm silicon single crystals to study the transient behavior of intrinsic point defects. It has been demonstrated that predicted point defect distributions are in good agreement with experimental results.     

Effect of the cylinder shape of a long-coned cyclone on the stable flow-field establishment

The flow characteristics and particle collection efficiencies of a long-cone cyclone with twice as long a conical section as that of the Stairmand cyclone were analyzed numerically to see the effect of the cylinder shape on the flow and collection performance. The three-dimensional flow field is obtained using the commercial package, FLUENT, and particle paths are calculated with the Lagrangean integration of the particle equation of motion. A number of turbulence models were tested, and it was confirmed that only the second-order Reynolds stress model gave reasonable results for the flow velocity profile.It is also shown that the shape of the core-annulus interface is important for the overall flow and collection characteristics, and the interface shape is in turn strongly affected by the distance from the bottom of the inlet to the cylinder-cone junction. By adjusting the diameters of the cylinder and the view finder with the mass flux and inlet area kept constant, the shape of the core-annulus interface could be changed. As a result, the short-circuiting of the inlet flow to the view finder and the total pressure drop could be reduced by properly adjusting the cylinder body diameter.     

Polyol synthesis of reduced graphene oxide supported platinum electrocatalysts for fuel cells: Effect of Pt precursor,support oxidation level and pH

In this work, a comprehensive study on the polyol synthesis of platinum supported on reduced graphene oxide (Pt/rGO) catalysts, including both ex-situ and in-situ characterizations of the prepared Pt/rGO catalysts, was performed. The polyol synthesis was studied considering the influence of the platinum precursor, oxidation level of graphite oxide and pH of reaction medium. The as-prepared catalysts were analyzed using thermo-gravimetric (TG) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and cyclic voltammetry (CV). The best results in terms of platinum particle size and distribution were obtained when the synthesis was performed in acidic medium, using chloroplatinic acid as precursor and using graphene oxide with high oxidation level. The most promising graphene-supported catalyst was used to prepare a polymer electrolyte membrane fuel cell electrode. The membrane electrode assembly (MEA) prepared with graphene-based electrode was compared with a MEA prepared with catalyst based on commercial platinum supported in carbon black (Pt/C). Single cell characterization included polarization curves and in-situ electrochemical impedance spectroscopy (EIS). The graphene-based electrode presented promising albeit unstable electrochemical performance due to water management issues. Additionally, EIS measurements revealed that the MEA made with Pt/rGO catalyst presented a lower mass transport resistance than the commercial Pt/C.     

Correlation Between Pre-annealing Temperature and {110}〈001〉 Annealing Texture in C- and Al-Free Fe-3 Pct Si-0.1 Pct Mn-0.002 Pct S Electrical Steel

In C- and Al-free electrical steel, the increase in primary grain size with increasing pre-annealing temperature causes the transition in annealing texture after final annealing from {110} + {100} to {110}. The strip pre-annealed at 1073 K (800 °C) shows a low magnetic induction B₈(T) of 1.784 T after final annealing. The strip pre-annealed at 1223 K (950 °C) shows a sharp {110}〈001〉 Goss texture, producing a high magnetic induction B₈(T) of 1.914 T comparable to that of the conventional electrical steels.     

Dynamic modeling of paper drying processes

A dynamic model describing the behavior of a multi-cylinder drying section in paper production plants was developed based on the mass and heat balances around drying cylinders. The balance equations consist of sets of differential equations describing heat and mass transfer around the canvas, the web and the drying cylinders. Values of cylinder temperatures and moisture contents were estimated and compared with operation data. To obtain further information for energy consumption, the generation of entropy at each drying cylinder was investigated based on the model developed.     

Factors Affecting Quality of Dried Low-Rank Coals

The chemical and physical properties of coal are strongly affected by the upgrading process employed. For high-moisture coals, upgrading involves thermal dehydration to improve the calorific value of the coal on mass basis. This study evaluates the feasibility of upgrading a low-rank/grade coal using the oven drying method. The objective of this research work is to study the drying characteristics of low-rank coals and to understand the factors affecting the quality of dried low-rank coals. This article describes laboratory experiments conducted on the characterization of the low-rank coals before and after the drying process. The results on drying kinetics, re-absorption of coal samples, and proximate analysis of coal samples before and after drying are discussed. It was found that the upgrading process produced coal with better heating value and combustion characteristics than those of the raw coal samples.     

Recent progress and perspectives on atomic-layer-deposited semiconducting oxides for transistor applications

This paper reviews recent developments in the fabrication of high-performance n-channel metal-oxide thin-film transistors (TFTs) through atomic-layer deposition (ALD), which are now attracting attention due to their potential for use in augmented and virtual reality, ultra-high-definition organic light-emitting diodes, and flexible electronics. Recent trends in research on TFT backplanes for display applications are provided in the introduction. In the main section, ALD-derived n-type oxides serving as active layers are classified into binary, ternary, and quaternary systems, and recent developments and critical issues in n-channel oxide TFTs are described. The performance of n-channel oxide TFTs can be boosted through advanced architectures, including stacked heterojunction channels using two-dimensional electron gases, and the introduction of high-k dielectric such as ALD-derived hafnium oxide, which is highlighted in this review. Finally, progress in p-channel ALD-derived oxide TFTs is briefly addressed with respect to complementary metal–oxide-semiconductor applications.     

Engineering III–V Semiconductor Nanowires for Device Applications

III–V semiconductor nanowires offer potential new device applications because of the unique properties associated with their 1D geometry and the ability to create quantum wells and other heterostructures with a radial and an axial geometry. Here, an overview of challenges in the bottom-up approaches for nanowire synthesis using catalyst and catalyst-free methods and the growth of axial and radial heterostructures is given. The work on nanowire devices such as lasers, light emitting nanowires, and solar cells and an overview of the top-down approaches for water splitting technologies is reviewed. The authors conclude with an analysis of the research field and the future research directions.     

Nonlinear Control of Magnetic Bearings

In this paper, recent results controling nonlinear systems with output tracking error constraints are applied to the design of new tracking controllers for magnetic bearings. The proposed controllers can force the rotor to track a bounded and sufficiently smooth refer-ence trajectory asymptotically and guarantee non-contactedness be-tween the rotor and the stator of the magnetic bearings. Simulation results are included to illustrate the effectiveness of the proposed con-trollers.