Numerical investigation of flow in a channel obstructed by an array of square rods (2nd report,Investigation of a criterion for judging the uniqueness and validity of numerical results)

Two‐dimensional numerical computation is performed for unsteady laminar flow. Spatially periodic boundary conditions are adopted in the streamwise direction, and in particular, a criterion for judging the uniqueness of the numerical solution is studied. The following results were obtained. When the numerical result fluctuates with the computational domain size, various low‐frequency components are markedly observed in the streamwise velocity of the calculated result. Compared with the channel flow obstructed by a single rod of the same size, the intensities of velocity fluctuation in this study are relatively high, and their distribution throughout the flow field is rather uniform. The spatially averaged kinematic energy of the velocity fluctuation is adopted as a key parameter, and a discrimination map of the uniqueness of the numerical solution is presented using a timescale ratio between mean flow and velocity fluctuation, the rod pitch, and the blockage ratio. The timescale ratio is well correlated with a geometric parameter obtained from the flow configuration, and the discrimination map can be converted such that the geometric parameter and the channel Reynolds number describe it. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(3): 113–126, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20152     

Solar energy powered Rankine cycle using supercritical CO2

A solar energy powered Rankine cycle using supercritical CO₂ for combined production of electricity and thermal energy is proposed. The proposed system consists of evacuated solar collectors, power generating turbine, high-temperature heat recovery system, low-temperature heat recovery system, and feed pump. The system utilizes evacuated solar collectors to convert CO₂ into high-temperature supercritical state, used to drive a turbine and thereby produce mechanical energy and hence electricity. The system also recovers heat (high-temperature heat and low-temperature heat), which could be used for refrigeration, air conditioning, hot water supply, etc. in domestic or commercial buildings. An experimental prototype has been designed and constructed. The prototype system has been tested under typical summer conditions in Kyoto, Japan; It was found that CO₂ is efficiently converted into high-temperature supercritical state, of while electricity and hot water can be generated. The experimental results show that the solar energy powered Rankine cycle using CO₂ works stably in a trans-critical region. The estimated power generation efficiency is 0.25 and heat recovery efficiency is 0.65. This study shows the potential of the application of the solar-powered Rankine cycle using supercritical CO₂.     

Blue sensitizers for solar cells: Natural dyes from Calafate and Jaboticaba

Blue-violet anthocyanins from Jaboticaba (Myrtus cauliflora Mart) and Calafate (Berberies buxifolia Lam) were employed as TiO₂ dye-sensitizers. Solar cells sensitized by Jaboticaba extracts achieved up to J_sc=9.0 mA cm⁻², V_oc=0.59 V, P_max=1.9 mW cm⁻² and ff=0.54, while for Calafate sensitized cells the values determined were up to J_sc=6.2 mA cm⁻², V_oc=0.47 V, P_max=1.1 mW cm⁻² and ff=0.36. Other natural dyes were evaluated without significant photocurrent, demonstrating that only selected extracts are capable of converting sunlight in electricity. The results obtained with extracts of Jaboticaba and Calafate show a successful conversion of visible light into electricity by using natural dyes as wide band-gap semiconductor sensitizers in dye-sensitized solar cells. It also represents an environmentally friendly alternative for dye-sensitized solar cells with low cost production and an excellent system for educational purposes.     

Spectral properties of nanoengineered Ag/Au bilayer rods fabricated by electron beam lithography

Ag/Au bimetallic nanoparticles possess the combinatory advantages of Au and Ag nanoparticles and can also be utilized to tune the properties of localized surface plasmon resonance. Ag/Au bilayer nanorods were prepared by electron beam lithography, and their spectral properties were investigated. Compared with Ag monolayer nanorods, Ag/Au bilayer nanorods show broader localized surface plasmon resonance bands, and the longitudinal mode and transverse mode localized surface plasmon bands show blueshift and redshift, respectively. The maximum near-field intensity of the longitudinal mode of the Ag/Au nanorod is less than half that of the Ag/Au nanorod without gold layer. Shape-induced modification of Ag/Au bilayer nanorods on their spectral properties was also discussed.     

Landslide susceptibility zonation study using remote sensing and GIS technology in the Ken-Betwa River Link area,India

The 231 km long Ken-Betwa River Linking canal will transfer 1,020 hm³ of surplus water from the Ken River to the deficit Betwa River basin. The landslide susceptibility zonation map of the river link has been assessed using remote sensing data in GIS. Various thematic maps such as geology, land use/land cover, lineament, drainage, slope, aspect, normalized difference vegetation index and soil type were generated from the Landsat Thematic Mapper 5 satellite data of 2005, the Survey of India topographic sheets, Shuttle Radar Topographic Mission Digital Elevation (SRTM-DEM) data and other existing maps. Numerical rating schemes were used for ranking the thematic layers. The results were supported with the rainfall data, groundwater level data and a petrological study of rock thin sections. In addition to providing valuable information for project decision-makers, the results will assist in slope management and land use planning in the area.     

Evaluation of self-controllability of LMFRs against ATWS

This paper describes a simple and general method to evaluate inherent and passive safety characteristics of fast reactors that uses self-controllability limit lines. The self-controllability limit lines are derived analytically for the extreme conditions such as sodium boiling or fuel melting as linear relationships among the total reactivity, effective coolant and fuel reactivites. The analytically obtained self-controllability limit lines are compared to those obtained by numerical result from the LMFR plant system transient analysis. For a given set of various reactivity coefficients of any actual LMFRs, judgement is made on whether the reactor can maintain the core integrity under ATWS conditions.     

Effects of hypokalaemia on arrhythmogenic risk of quinidine in rats

Plasma potassium concentration plays an important role in the induction of arrhythmia and is closely related to the arrhythmogenicity of various drugs. We quantitatively analyzed the influence of plasma potassium concentration on QT intervals before drug administration and on drug-induced QT prolongation, to estimate the risk of drug-induced arrhythmia under hypokalaemic conditions. The hypokalaemic models were produced by intraperitoneal administration of furosemide and hydrochlorothiazide in male Sprague-Dawley rats. The relationship between the changes in QT intervals and time profiles of plasma quinidine (QND) concentration were analyzed during constant intravenous infusion of QND (10 or 30 mg/kg/h) and post infusion in normal and hypokalaemic rats. The plasma QND concentration reached the therapeutic range (3-7 microg/ml) at the high infusion rate (30 mg/kg/h). No pharmacokinetic differences between normal and hypokalaemic rats were observed. QND induced QT prolongation in parallel with the plasma concentration without hysteresis. Although the potency of QND for QT prolongation was not affected by hypokalaemia, the QT intervals before drug administration were significantly prolonged in hypokalaemic rats (65.90 +/- 1.40 vs 56.60 +/- 0.748 msec, mean +/- SEM, p < 0.0001). Thus, the prolongation of QT intervals before drug administration may act as a risk factor of arrhythmia under hypokalaemic conditions.     

Noise suppression effect in an avalanche multiplication photodiode operating in a charge accumulation mode

A pixel configuration available to solid-state imagers using an avalanche multiplication photodiode operated in a charge accumulation mode, with each pixel as a photo-element, is proposed and stable avalanche multiplication gains over several tens are demonstrated by using a test circuit composed of discrete elements, equivalent to the pixel configuration. Moreover, it is found that the self-quenching effects inherent to the APD operating in this mode suppress the reset or avalanche induced excess noises, predominant in readout process and in charge accumulation process, respectively. These results are advantageous for a solid-state imager since the use of the avalanche multiplication simultaneously satisfies the two requirements of high sensitivity and wide dynamic range.<>