Mechanistic modeling for ring-type boiling water reactor fuel spacer design (3) run-off effect and model formulation

The fuel spacer is one of the components of a fuel rod bundle and its role is to maintain an appropriate rod-to-rod clearance. The fuel spacer influences the liquid film flow distribution in the fuel rod bundle, so that the spacer geometry has a strong effect on thermal hydraulic characteristics of BWR such as critical power and pressure drop in the fuel bundle. In this paper, liquid film flow characteristics were experimentally investigated in a circular channel with ring-type spacers using air and water as test fluids in order to be compared with the analytical results introducing the mechanistic spacer model. The spacer model was composed of three effects; the drift flow effect, the narrow channel effect and the run-off effect. The drift flow effect and the narrow channel effect were discussed in the previous works and the run-off effect is done in this paper. This paper shows the formulation around the spacer with use of the three effects. The proposed model explains well the experimental results of liquid film flow rates and thickness carried out in reference to the spacer thickness, the gap between the channel wall and the spacer.     

Flame propagation through concentration gradient

IntroductionIn the matter of internal combustion engine, thesimultaneous reduction of fuel consumption andpollutant emission are required. Pedial premixedcombustion is expected to be a combustion method torealize this. The combustion method has both theadvantage of premixed combustion (low environmentalpollution ) and that of diffusive combustion (highefficiency ). The method is already used in the directinjection gasoline engine and in diesel engine with twostage injection or spray atomizatio…     

Sol-gel processing of carbidic glasses

Carbon incorporation into the silicate network results in the formation of rigid carbidic glasses with improved physical, mechanical and thermal properties. This generated great interest in the development of these heteroatom structured materials through different processing routes. In the present studies, sol-gel processing has been used to prepare silicon based glasses, especially oxycarbides through organic-inorganic hybrid gels by hydrolysis-condensation reactions in silicon alkoxides, 1,4-butanediol and furfuryl alcohol with an aim to introduce Si-C linkages in the precursors at sol level. The incorporation of these linkages has been studied using IR and NMR spectroscopy. These bonds, so introduced, are maintained throughout the processing, especially during pyrolysis to high temperatures. In FFA-TEOS system, copolymerization with optimized mol ratio of the two results in resinous mass. This precursor on pyrolysis to 1000°C results in Si-O-C type amorphous solid black mass. XRD studies on the materials heated to 1400°C exhibit presence of crystalline Si-C and cristobalites in amorphous Si-O-C mass. In organic-inorganic gel system, the pyrolysed mass exhibits phase stability up to much higher temperatures. The carbidic materials so produced have been found to exhibit good resistance against oxidation at 1000°C. Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore     

Suppressive effect of magnesium oxide materials on cadmium accumulation in winter wheat grain cultivated in a cadmium-contaminated paddy field under annual rice–wheat rotational cultivation

The effectiveness of two kinds of magnesium oxide (MgO) materials, commercial MgO (2250 kg ha⁻¹) and a material derived from MgO and magnesium silicate minerals named ‘MgO-SH-A’ (2250 and 4500 kg ha⁻¹1), in suppression of uptake and accumulation of cadmium (Cd) into grain of winter wheat (Triticum aestivum L. cv. Ayahikari) was examined in a Cd-contaminated alluvial paddy field under annual rice–wheat rotational system. The MgO materials were mixed into the plough-layer soil only once prior to the preceding rice cultivation. Cadmium concentration in wheat grain produced from the non-amendment control exceeded the maximum limit of Cd in wheat grain adopted by FAO/WHO (0.2 mg kg⁻¹). All of the treatments with the MgO materials significantly lowered plant available Cd fraction in the plough-layer soil. However, only the treatment with the commercial MgO at 2250 kg ha⁻¹ produced wheat grain whose Cd concentration was not only significantly lower than that from the control but also less than 0.2 mg kg⁻¹. It is suggested that the significant suppressive effect of the commercial MgO on Cd accumulation in wheat grain would be mainly attributed to its high soil neutralizing capacity as compared to that of MgO-SH-A.     

Tunneling currents in In0.53Ga0.47As homojunction diodes and design of InGaAs/InP hetero-structure avalanche photodiodes

Tunneling currents in InGaAs homojunctions were studied from measurements of temperature dependence of breakdown voltage, current-voltage characteristics, tunneling effective mass, and noise spectrum. Zener emission dominates the reverse current prior to avalanche breakdown in the carrier concentration region of >10¹⁵ cm^?3 and restricts the avalanche gain in InGaAs homojunctions. An InGaAs/InP hetero-structure having a p-n junction in the InP layer was studied to reduce dark currents caused by Zener emission. A design chart to aid in the realization of a high performance APD is discussed.     

Development of novel fibers for telecoms application

This paper reviews the current situations of optical fibers used for terrestrial and submarine transmission systems as well as up-to-date R&;D on these fibers. The current fibers include standard single mode fibers (SMFs), non-zero dispersion shifted fibers (NZ-DSFs), and dispersion managed lines (DMLs). Even though these fibers show quite high and matured properties, the internet traffic is continuously growing, and around 2015–2020, it is expected that the current transmission fibers would become inadequate. To prepare for the future ultra high-capacity transmission, there are three important R&;D directions for transmission fibers. (1) Reducing non-linearity by means of enlarging Aeff and/or reducing attenuation loss. It is very important in the case of transmission systems using new multi-level signal formats. (2) Expanding the transmission band more than the current C- and/or L-Band by utilizing new transmission fibers. For example, holey fibers (HFs), which have an endlessly single mode (ESM) property, are one of the interesting candidates of the new transmission fibers. (3) Using Space Division Multiplexing (SDM) by using multi-core fibers. The multi-core fiber literally multiples the core number within a fiber dimension, which enables multiple transmission capacity per one fiber. In addition to the developments of transmission fibers, component fibers have also been studied and developed. Examples of R&;D on these component fibers will be also discussed in the latter part of this paper.     

Formation of metastable conductive nanowire in a thiospinel compound CuIr2S4 induced by ion irradiation

We observed an increase in the conductivity of a thiospinel compound, CuIr₂S₄, induced by H⁺ and He⁺ irradiation with energies of 1-2 MeV. It was indicated that the metastable conductive phase was produced by electronic excitation due to the ion beam and this phase was similar to the X-ray-induced phase. Conductivity as a function of ion fluence was analyzed by a simple model where the ion-induced change occurred in a cylindrical region around an ion trajectory. The cross-sectional area of the cylinder was obtained by analyzing the conductivity as a function of ion fluence for each ion, and it was found that an impinging ion produced a nanowire in the conductive phase. In addition, the yield of the Ir dimer displacement, which was related to the increase in conductivity, was considerably high. The ion irradiation effect reported in this paper is unique with regard to the high yield and low linear energy transfer (LET) in the formation of the conductive-phase nanowire. Both these unique aspects could be ascribed to the low band-gap energy and strong electron-lattice interaction of this compound.     

Effect of Carrier Frequency and Circuit Resistance on Iron Loss of Non‐Oriented Electrical Steel Sheet under Single‐Phase Full‐Bridge PWM Inverter Excitation

Because of the development of power electronics technology, pulse width modulation (PWM) inverters are now being used to drive motors in order to achieve precise and energy‐efficient control. Precise estimation of the increase in iron loss due to the high harmonic components of flux, including the carrier frequency, is important in the design of motors excited by a PWM inverter. We measured the iron losses of non‐oriented electrical steel sheets that were excited using a single‐phase full‐bridge PWM inverter, and examined the influence of the carrier frequency and circuit resistance on the iron loss. We showed that the iron loss increased because of the generation of minor loops when the circuit resistance was high. Therefore, the circuit resistance should be decreased in an actual motor system.     

Network Expansion Planning Using Improved Controlled NSGA‐II

This paper presents the application of multiobjective optimization methods to network expansion planning. Distribution network expansion planning minimizes system cost and distribution loss while satisfying the constraints. Problem formulation yields combinatorial optimization problems that are difficult to solve due to their complexity. This research applies a genetic algorithm, which is a meta‐heuristics method. The present study proposes a new method of multiobjective optimization: NSGA‐II, SPEA2, and Controlled NSGA‐II are assumed to be the best methods now. The proposed method introduces the concept of a linkage identification genetic algorithm, enabling more efficient searching than methods hitherto known. In the past, most research on network expansion planning did not include the load curve. This research demonstrates that the investigation must include the load curve. It also proposes a new method of search including the load curve.     

Zero‐attracting variable‐step‐size least mean square algorithms for adaptive sparse channel estimation

Recently, sparsity‐aware least mean square (LMS) algorithms have been proposed to improve the performance of the standard LMS algorithm for various sparse signals, such as the well‐known zero‐attracting LMS (ZA‐LMS) algorithm and its reweighted ZA‐LMS (RZA‐LMS) algorithm. To utilize the sparsity of the channels in wireless communication and one of the inherent advantages of the RZA‐LMS algorithm, we propose an adaptive reweighted zero‐attracting sigmoid functioned variable‐step‐size LMS (ARZA‐SVSS‐LMS) algorithm by the use of variable‐step‐size techniques and parameter adjustment method. As a result, the proposed ARZA‐SVSS‐LMS algorithm can achieve faster convergence speed and better steady‐state performance, which are verified in a sparse channel and compared with those of other popular LMS algorithms. The simulation results show that the proposed ARZA‐SVSS‐LMS algorithm outperforms the standard LMS algorithm and the previously proposed sparsity‐aware algorithms for dealing with sparse signals. Copyright © 2015 John Wiley & Sons, Ltd.