Stabilization of anatase phase by uncompensated Ga-V co-doping in TiO2: A structural phase transition,grain growth and optical property study

Uncompensated Ga-V co-doped TiO₂ samples have been prepared by modified sol-gel process. Inhibition of phase transition due to co-doping is confirmed by X-ray diffraction measurement. Activation of phase transition increases from 120?kJ/mol (x?=?0) to 240?kJ/mol (x?=?0.046) due to Ga-V incorporation. In anatase phase, lattice constant increases by the effect of Ga³⁺ interstitials. This results in inhibition of phase transition. Anatase phase becomes stable up to ~ 650?°C in co-doped sample whereas for pure TiO₂ phase transition starts in between 450 and 500?°C. High-resolution transmission electron microscope image shows particle size decreases in anatase phase due to co-doping. Increasing strain due to Ga-V incorporation results in reducing crystallite size. Brunauer–Emmett–Teller analysis shows that surface increases from 4.55?m²/g (pure TiO₂) to 96.53?m²/g (x?=?0.046) by Ga-V incorporation. In rutile phase, grain growth process is enhanced mainly due to the effect of Vanadium and particles show a rod-like structure with majority {110} facets. Bandgap decreases in both phases and reduced to visible light region. For charge balance in uncompensated Ga-V co-doped sample, structural distortion created in the lattice by combining effect of substitution, interstitials and oxygen vacancies, which results in stabilization of anatase phase and reducing of bandgap.     

Calculation of dry out and post-dry out heat transfer in rod bundles using a three field model

The critical heat flux (CHF) condition is an important parameter in the design and operation of nuclear reactor fuel rod assemblies. It has traditionally been evaluated using look-up tables or empirical correlations. In the present paper, a set of relations, in the form of a one-dimensional three-field model, is presented which enables a mechanistic prediction of high-quality CHF known as dry out. This also allows a more fundamental treatment of post-dry out heat transfer. The ensemble of relations is validated by comparing the predictions with data obtained from the TPTF test series of JAERI and the THTF test series of ORNL. The rod bundles have been modelled on a sub-channel basis. The effect of spacer grids on the flow and heat transfer has been studied by including their geometrical characteristics only. Good predictions of the dry out location and the post-dry out variation of the rod temperature are obtained over the range of parameters investigated in these tests, namely, in the pressure range of 30-130 bar, mass flux range of 50-800 kg/m² s and inlet condition ranging from sub-cooled to an inlet quality of 0.89.     

Equilibrium considerations in aerosol formation during sodium combustion

Combustion of liquid sodium is of interest in the safety assessment of liquid metal cooled fast breeder reactor systems. In the present study, a detailed thermodynamic analysis of sodium-air system has been carried out for equivalence ratios in the range of 0.1–1.9 and for flame temperatures ranging from 1100 to 1950 K. In addition to this, decomposition calculations presented for product aerosols such as sodium oxide (Na₂O), sodium dioxide (Na₂O₂) and sodium hydroxide (NaOH) in normal oxygen and oxygen-deficient conditions (which are some form of phase diagrams of these aerosols) are used rigorously to find out the predominant aerosol that should be present in and outside the burn pan for a pool fire of liquid sodium. The conditions of occurrence of various sodium oxides under two different fire conditions namely pool and jet fires have been worked out. It is established that heterogeneous reactions involving sodium oxide are responsible for the formation of sodium dioxide and sodium hydroxide. It is necessary to take account of the rates of these heterogeneous reactions as well as the equivalence ratio-dependent decomposition calculations to correctly estimate the aerosol product mix in practical situations.     

Augmented infinitesimal perturbation analysis: An alternate explanation

Augmented infinitesimal perturbation analysis (APA) was introduced by Gaivoronski [1991] to increase the purview of the theory of Infinitesimal Perturbation Analysis (IPA). In reference [Gaivoronski 1991] it is shown that an unbiased estimate for the gradient of a class of performance measures of DEDS represented bygeneralized semi-Markov processes (GSMPs) (cf. [Glynn 1989] can be expressed as a sum of an IPA-estimate and a term that takes into account the event order changes. In this paper we present an alternate approach to establishing the result of Gaivoronski, and from this we derive a necessary and sufficient condition for the validity of the IPA algorithm for this class of performance measures. Finally we validate our results by simulation examples.This research was supported by the National Science Foundation under grant number ECS-85-15449, Office of Naval Research Grants Nos. N00014-90-K-1093 and N00014-89-J-1023 and by Army Grant No. DAAL-03-86-K-0171.     

The relevance of short communication in scholarly journals: An empirical study

This study aims to examine whether rapid communications exert more influence/impact on subsequent research. Citation analysis of Short Communications (SCs) and Main Articles (MAs) from 1983 and 1990 for 5 high impact biomedical journals was carried out for a five year period following publication. The mean citations cumulated for the five year period showed no consistent trend. Some journals showed more citations for SCs while some showed more for MAs. The mean citations (range) for SCs and MAs for the 1983 and 1990 papers respectively were as follows:Gene: 14.13 (0-61) and 38.79 (0-677), 9.73 (0-93) and 13.17 (0-44);Journal of Clinical Investigation (JCI): 79.77 (3-202) and 27.52 (0-86), 50.52 (0-254) and 33.53 (0-151);Journal of Experimental Medicine (JEM): 39.80 (0-200) and 49.20 (0-403), 47.26 (0-258) and 50.27 (0-173); andJournal of Biological Chemistry (JBC); 36.21 (0-380) and 19.67 (0-53), 37.19 (0-273) and 26.84 (0-185). SCs ofJournal of Cell Biology (JCB) had a mean citation of 25.84 per article with a range of 0-98, while the MAs had a mean citation of 33.13 with the range 4-122 during 1983-87. The citation peak was seen about three years after publication for all the journals during both the periods. The mean cumulative citations showed a progressive increase over the five years for both types of papers, in all journals and for both the 5 year periods. The initial differences observed persisted even four years after the year of publication. No significant differences were observed in the distribution of the cumulative 5 year citations between the SCs and MAs. An index of speed of citation per article showed no substantial differences between SCs and MAs with MAs showing an edge over SCs. Both MAs and SCs of all the journals showed nearly same average time per citation per article further confirming that the SCs do not enjoy the advantage of speedier citation. The results show that the generally perceived feeling of SCs getting cited more frequently and faster does not appear to be valid. Hence, the practice of publishing SCs on a priority basis is perhaps not warranted.     

Ordinal optimization of DEDS

In this paper we argue thatordinal rather thancardinal optimization, i.e., concentrating on finding good, better, or best designs rather than on estimating accurately the performance value of these designs, offers a new, efficient, and complementary approach to the performance optimization of systems. Some experimental and analytical evidence is offered to substantiate this claim. The main purpose of the paper is to call attention to a novel and promising approach to system optimization.This work is supported by NSF grants CDR-88-03012, DDM-89-14277, ONR contracts N00014-90-J-1093, N00014-89-J-1023, and army contracts DAAL-03-83-K-0171, DAAL-91-G-0194.     

A general method for resonance power supply analysis

The resonance power supply is widely used and proved to be an efficient method to supply accelerator magnets. The literature describes several power supply circuits, but no comprehensive theory of operation is presented. The authors present a mathematical method which describes the operation of the resonance power supply and its use for the accurate design of components     

Micro-kinetic modeling of NH3 decomposition on Ni and its application to solid oxide fuel cells

This paper presents a detailed surface reaction mechanism for the decomposition of NH₃ to H₂ and N₂ on a Ni surface. The mechanism is validated for temperatures ranging from 700 to 1500 K and pressures from 5.3 Pa to 100 kPa. The activation energies for various elementary steps are calculated using the unity bond index-quadratic exponential potential (UBI-QEP) method. Sensitivity analysis is carried out to study the influence of various kinetic parameters on reaction rates. The NH₃ decomposition mechanism is used to simulate SOFC button cell operating on NH₃ fuel.     

Feasibility of using ultrasound-assisted process for sulfur and ash removal from coal

The present work investigates utilization of ultrasound in reagent-based coal de-ashing and de-sulfurization. The coal under study was received from Girald mine, Rajasthan, India. Three different ultrasonic frequencies (25 kHz, Dual (58/192 kHz) and 430 kHz) and three reagents (HCl, HNO₃ and H₂O₂) were used. The study employed a Taguchi fractional-factorial L₂₇ DOE. Experimental data were used to derive an empirical model for the prediction of total sulfur removal. The model incorporates cavitational intensity, reagent concentration, sonication time, coal particle size and coal concentration as key parameters. Effects of above factors on reagent-based ultrasonic coal-desulfurization are presented here. An optimum set of process parameters are identified and validated. Larger-scale trial with high-ash and high-sulfur coals is strongly recommended.     

Laboratory evaluation of custom-designed surfactants to remediate NAPL source zones

Laboratory column studies were conducted using custom-designed anionic surfactants, the branched alcohol propoxylated sulfates, to evaluate their effectiveness in removing nonaqueous phase liquids (NAPLs) from both Ottawa sand and field alluvium. Surfactant efficacy was tested at temperatures ranging between 11 and 50 degrees C for contaminants such as tetrachloroethene (PCE), weathered gasoline, and Naval Special Fuel Oil. It has been shown that use of branched alcohol propoxylated sulfates can achieve very low final NAPL saturations even with recalcitrant NAPLs, while exhibiting low induced hydraulic gradients, low microemulsion viscosity, and minimal sorption on contaminated field soils. These custom-designed surfactants are effective with both dense NAPLs (DNAPLs) and light NAPLs. Finally, these surfactants were used to create neutrally buoyant microemulsions with a PCE DNAPL. The laboratory experiments show that these custom-designed, high-performance surfactants can be tailored to optimize contaminant solubility for specific field NAPLs.