Low temperature and self catalytic growth of ultrafine ITO nanowires by electron beam evaporation method and their optical and electrical properties

We report the self catalytic growth of Sn-doped indium oxide (ITO) nanowires (NWs) over a large area glass and silicon substrates by electron beam evaporation method at low substrate temperatures of 250-400 degrees C. The ITO NWs growth was carried out without using an additional reactive oxygen gas and a metal catalyst particle. Ultrafine diameter (similar to 10-15 nm) and micron long ITO NWs growth was observed in a temperature window of 300-400 degrees C. Transmission electron microscope studies confirmed single crystalline nature of the NWs and energy dispersive spectroscopy studies on the NWs confirmed that the NWs growth proceeds via self catalytic vapor-liquid-solid (VLS) growth mechanism. ITO nanowire films grown on glass substrates at a substrate temperature of 300-400 degrees C have shown similar to 2-6% reflection and similar to 70-85% transmission in the visible region. Effect of deposition parameters was systematically investigated. The large area growth of ITO nanowire films would find potential applications in the optoelectronic devices. (C) 2014 Elsevier Ltd. All rights reserved.

Formation of Prestellar Cores via Non-Isothermal Gas Fragmentation

Sheet-like clouds are common in turbulent gas and perhaps form via collisions between turbulent gas flows. Having examined the evolution of an isothermal shocked slab in an earlier contribution, in this work we follow the evolution of a sheet-like cloud confined by (thermal) pressure and gas in it is allowed to cool. The extant purpose of this endeavour is to study the early phases of core-formation. The observed evolution of this cloud supports the conjecture that molecular clouds themselves are three-phase media (comprising viz. a stable cold and warm medium, and a third thermally unstable medium), though it appears, clouds may evolve in this manner irrespective of whether they are gravitationally bound. We report, this sheet fragments initially due to the growth of the thermal instability (TI) and some fragments are elongated, filament-like. Subsequently, relatively large fragments become gravitationally unstable and sub-fragment into smaller cores. The formation of cores appears to be a three stage process: first, growth of the TI leads to rapid fragmentation of the slab; second, relatively small fragments acquire mass via gas-accretion and/or merger and third, sufficiently massive fragments become susceptible to the gravitational instability and sub-fragment to form smaller cores. We investigate typical properties of clumps (and smaller cores) resulting from this fragmentation process. Findings of this work support the suggestion that the weak velocity field usually observed in dense clumps and smaller cores is likely seeded by the growth of dynamic instabilities. Simulations were performed using the smooth particle hydrodynamics algorithm.

ADAPTATION OF MW LEVEL NATURAL GAS LEAN BURN ENGINE FOR PRODUCER GAS OPERATION A GRID CONNECTED POWER PLANT

Availability of producer gas engines at MW being limited necessitates to adapt engine from natural gas operation. The present work focus on the development of necessary kit for adapting a 12 cylinder lean burn turbo-charged natural gas engine rated at 900 kWe (Waukesha make VHP5904LTD) to operate on producer and set up an appropriate capacity biomass gasification system for grid linked power generation in Thailand. The overall plant configuration had fuel processing, drying, reactor, cooling and cleaning system, water treatment, engine generator and power evacuation. The overall project is designed for evacuation of 1.5 MWe power to the state grid and had 2 gasification system with the above configuration and 3 engines. Two gasification system each designed for about 1100 kg/hr of woody biomass was connected to the engine using a producer gas carburetor for the necessary Air to fuel ratio control. In the use of PG to fuel IC engines, it has been recognized that the engine response will differ as compared to the response with conventional fueled operation due to the differences in the thermo-physical properties of PG. On fuelling a conventional engine with PG, power de-rating can be expected due to the lower calorific value (LCV), lower adiabatic flame temperature (AFT) and the lower than unity product to reactant more ratio. Further the A/F ratio for producer gas is about 1/10th that of natural gas and requires a different carburetor for engine operation. The research involved in developing a carburetor for varying load conditions. The patented carburetor is based on area ratio control, consisting of a zero pressure regulator and a separate gas and air line along with a mixing zone. The 95 litre engine at 1000 rpm has an electrical efficiency of 33.5 % with a heat input of 2.62 MW. Each engine had two carburetors designed for producer gas flow each capable of handling about 1200 m3/hr in order to provide similar engine heat input at a lower conversion efficiency. Cold flow studies simulating the engine carburetion system results showed that the A/F was maintained in the range of 1.3 +/- 0.1 over the entire flow range. Initially, the gasification system was tested using woody biomass and the gas composition was found to be CO 15 +/- 1.5 % H-2 22 +/- 2% CH4 2.2 +/- 0.5 CO2 11.25 +/- 1.4 % and rest N-2, with the calorific value in the range of 5.0 MJ/kg. After initial trials on the engine to fine tune the control system and adjust various engine operating parameter a peak load of 800 kWe was achieved, while a stable operating conditions was found to be at 750 kWe which is nearly 85 % of the natural gas rating. The specific fuel consumption was found to be 0.9 kg of biomass per kWh.

Modeling of sonochemical decomposition of CCI4 in aqueous solutions

In the context of removal of organic pollutants from wastewater, sonolysis of CCl4 dissolved in water has been widely investigated. These investigations are either completely experimental or correlate data empirically. In this work, a quantitative model is developed to predict the rate of sonolysis of aqueous CCl4. The model considers the isothermal growth and partially adiabatic collapse of cavitation bubbles containing gas and vapor leading to conditions of high temperatures and pressures in them, attainment of thermodynamic equilibrium at the end of collapse, release of bubble contents into the liquid pool, and reactions in the well-mixed pool. The model successfully predicts the extent of degradation of dissolved CCl4, and the influence of various parameters such as initial concentration of CCl4, temperature, and nature of gas atmosphere above the liquid. in particular, it predicts the results of Hua and Hoffmann (Environ. Sci Technol, 1996, 30, 864-871), who found that degradation is first order with CCl4 and that Argon as well as Ar-O-3 atmospheres give the same results. The framework of the model is capable of quantitatively describing the degradation of many dissolved organics by considering all the involved species.

Analysis of a Filter Bag Reactor for gaseous pollution abatement

The conveying zone and the filter bag zone of a Filter Bag Reactor have been analysed as individual reactors. The gas and solid particles flow almost in plug flow through the pneumatic conveying section. In the filter bag the height of the packed column varies with time, a cell model has been used to calculate the concentration of outgoing stream. The total conversion obtained is the sum of conversions in each section of the reactor.

On the Purity of Atmospheric Glow-Discharge Plasma

Purity of the glow-discharge plasma at atmospheric pressure for surface modification applications is always debatable, since it works at ambient atmosphere. We have demonstrated on the use of optical emission spectroscopy to test the purity of this kind of plasma. The effect of gas flow pattern, nature of gas, and its flow rate on the plasma chemistry was studied. The importance of proper system design in maintaining a uniform flow of heavy and inert gases as carrier gas in atmospheric glow-discharge plasma was confirmed. The surface of a plasma-treated PET sample was analyzed using X-ray photoelectron spectroscopy to verify the studies on plasma purity done using emission spectrum.

Thermal decomposition of rare-earth trioxalatocobaltates

The thermal decomposition of rare-earth trioxalatocobaltates LnCo(C2O4)3 · x H2O, where Ln = La, Pr, Nd, has been studied in flowing atmospheres of air/oxygen, argon/ nitrogen, carbon dioxide and a vacuum. The compounds decompose through three major steps, viz. dehydration, decomposition of the oxalate to an intermediate carbonate, which further decomposes to yield rare-earth cobaltite as the final product. The formation of the final product is influenced by the surrounding gas atmosphere. Studies on the thermal decomposition of photodecomposed lanthanum trioxalatocobaltate and a mechanical mixture of lanthanum oxalate and cobalt oxalate in 1 : 2 molar ratio reveal that the decomposition behaviour of the two samples is different. The drawbacks of the decomposition scheme proposed earlier have been pointed out, and logical schemes based on results obtained by TG, DTA, DTG, supplemented by various physico-chemical techniques such as gas and chemical analyses, IR and mass spectroscopy, surface area and magnetic susceptibility measurements and X-ray powder diffraction methods, have been proposed for the decomposition in air of rare-earth trioxalatocobaltates as well as for the photoreduced lanthanum salt and a mechanical mixture of lanthanum and cobalt oxalates.

Thermal decomposition of titanyl oxalates-I : Barium titanyl oxalate

Thermal decomposition of barium titanyl oxalate tetrahydrate (BTO) has been investigated employing TGA, DTG and DTA techniques and gas and chemical analysis. The decomposition proceeds through five steps and is not affected much by the surrounding gas atmosphere. The first step which is the dehydration of the tetrahydrate is followed by a low-temperature decomposition of the oxalate groups. In the temperature range 190–250°C half a mole of carbon monoxide is evolved with the formation of a transient intermediate containing both oxalate and carbonate groups. The oxalate groups are completely destroyed in the range 250–450°C, resulting in the formation of a carbonate which retains free carbon dioxide in the matrix. The trapped carbon dioxide is released in the temperature range of 460–600°C. The final decomposition of the carbonate takes place between 600–750°C and yields barium titanate. The i.r. spectra, surface area measurements and X-ray, powder diffraction data support entrapment of carbon dioxide in the matrix.

Anderson transitions in Ln1-xSrxCoO3 (Ln=Pr or Nd)

Electrical conductivity measurements show that Ln1-xSrxCoO3, (Ln = Pr or Nd) undergoes a non-metal-metal transition when x-0 3. The d.c. conductivity of compositions with 0and the a.c. conductivity data follow the \omega law with \delta in the range 0.6-0.8. Surprisingly, however, \delta seems to increase with increasing temperature. Thermopower measurements show clear evidence for a change in the mechanism of conduction (around 350 K) from variable range hopping to transport at Ec. All these transport properties suggest that Co4+ ions in Ln1-xSrxCoO3 (0gas and that the states at the Fermi energy are Anderson localized.

CFD analysis of high frequency miniature pulse tube refrigerators for space applications with thermal non-equilibrium model

High frequency, miniature, pulse tube cryocoolers are extensively used in space applications because of their simplicity. Parametric studies of inertance type pulse tube cooler are performed with different length-to-diameter ratios of the pulse tube with the help of the FLUENT (R) package. The local thermal non-equilibrium of the gas and the matrix is taken into account for the modeling of porous zones, in addition to the wall thickness of the components. Dynamic characteristics and the actual mechanism of energy transfer in pulse are examined with the help of the pulse tube wall time constant. The heat interaction between pulse tube wall and the oscillating gas, leading to surface heat pumping, is quantified. The axial heat conduction is found to reduce the performance of the pulse tube refrigerator. The thermal non-equilibrium predicts a higher cold heat exchanger temperature compared to thermal equilibrium. The pressure drop through the porous medium has a strong non-linear effect due to the dominating influence of Forchheimer term over that of the linear Darcy term at high operating frequencies. The phase angle relationships among the pressure, temperature and the mass flow rate in the porous zones are also important in determining the performance of pulse tuberefrigerator.

Solubility of sulfur dioxide at low partial pressures in dilute sulfuric acid solutions

Equilibrium of dissolution of sulfur dioxide at ppm levels in aqueous solutions of dilute sulfuric acid is analyzed, and a general expression is derived relating the total concentration of sulfur dioxide in the liquid phase to the partial pressure of SO2 in the gas and to the concentration of sulfuric acid in the solution. The equation is simplified for zero and high concentrations of the acid. Experiments at high concentrations of sulfuric acid have enabled the direct determination of Henry’s constant and its dependency on temperature. Heat of dissolution is -31.47 kJ/mol. Experiments in the absence of sulfuric acid and the related simplified expression have led to the determination of the equilibrium constant of the hydrolysis of aqueous sulfur dioxide and its temperature dependency.The heat of hydrolysis is 15.69 kJ/mol. The model equation with these parameters predicts the experimental data of the present work as well as the reported data very well.

Global solutions describing the collapse of a spherical or cylindrical cavity

The collapse of a spherical (cylindrical) cavity in air is studied analytically. The global solution for the entire domain between the sound front, separating the undisturbed and the disturbed gas, and the vacuum front is constructed in the form of infinite series in time with coefficients depending on an ldquoappropriaterdquo similarity variable. At timet=0+, the exact planar solution for a uniformly moving cavity is assumed to hold. The global analytic solution of this initial boundary value problem is found until the collapse time (=(gamma–1)/2) for gamma le 1+(2/(1+v)), wherev=1 for cylindrical geometry, andv=2 for spherical geometry. For higher values of gamma, the solution series diverge at timet — 2(beta–1)/ (v(1+beta)+(1–beta)2) where beta=2/(gamma–1). A close agreement is found in the prediction of qualitative features of analytic solution and numerical results of Thomaset al. [1].

Star formation in giant extragalactic H II regions

Star formation properties in Giant Extragalactic H II Regions (GEHRs) are investigated using optical photometry and evolutionary population synthesis models. Photometric data in $BVR$ bands and in the emission line of H-alpha are obtained by CCD imaging at Vainu Bappu Observatory, Kavalur. Aperture photometry is performed for 180 GEHRs in galaxies NGC 1365, 1566, 2366, 2903, 2997, 3351, 4303, 4449, 4656 and 5253. Thirty six of these GEHRs having published spectroscopic data are studied for star formation properties. The population synthesis model is constructed based on Maeder's stellar evolutionary and Kurucz stellar atmosphere models, to synthesize observational quantities of embedded clusters in GEHRs. The observed H-alpha luminosity is a measure of the number of massive stars while the contribution to BVR bands is from intermediate mass (5-15 solar mass) stars when the cluster is young and from evolving supergiants when the cluster is old (age >/= 6~Myr). Differential reddening between gas and embedded stars is essential to constrain the dereddened cluster colors within the range of youngest clusters. Obscuring dust closely associated with gas, which is distributed in filaments and clumps, as in the case of 30 Doradus, is the most likely configuration giving rise to net reduction of extinction towards stars. The fraction of the stellar photons escaping the nebula unattenuated is estimated to be 50%. GEHRs are rarely found to be simple systems containing stars from single generation. In the present sample such regions in addition to being older than 3~Myr, have their Lyman continuum luminosity reduced by as much as 60%, compared to the observed $B$ band luminosity for a normal IMF. The missing ionizing photons may be escaping the nebula, leading to the ionization of extra-H II region ionized medium. Co-existence of young (age and old populations (~10~Myr; Red Supergiants) is found to be common in GEHRs. The emission and continuum knots are seen spatially separated (40-100 pc) on CCD images in NGC 2997, 4303 and 4449 and may be direct evidences for the co-existence of young and old populations in giant star forming complexes. Triggering of star formation from earlier bursts is the most likely cause of new generation of stars, and may be a common phenomenon in GEHRs. Spatial separation between the young and old stars (~30 pc) had been earlier reported in 30 Doradus. Thus GEHRs in nearby galaxies share many of the properties shown by 30 Dor, the nearest GEHR. (SECTION: Dissertation Summaries)

Injection cooling of blunt bodies flying at high Mach numbers

A study of transpiration cooling of blunt bodies such as a hemicylinder is made by solving Navier-Stokes equations. An upwind, implicit time-marching code is developed for this purpose. The study is conducted for both perfect-gas and real-gas (chemical equilibrium) flows. Investigations are carried out for a special wall condition that is referred to as no heat flow into the wall condition. The effects of air injection on wall temperature are analyzed. Analyses are carried out for Mach numbers ranging between 6-10 and Reynolds numbers ranging between 10(6)-10(7). Studies are made for spatially constant as well as spatially varying mass injection rate distributions, White cold air injection reduces the wall temperature substantially, transpiration cooling is relatively less effective when the gas is in chemical equilibrium.

On generating optimal signal probabilities for random tests: A genetic approach

Genetic Algorithms are robust search and optimization techniques. A Genetic Algorithm based approach for determining the optimal input distributions for generating random test vectors is proposed in the paper. A cost function based on the COP testability measure for determining the efficacy of the input distributions is discussed, A brief overview of Genetic Algorithms (GAs) and the specific details of our implementation are described. Experimental results based on ISCAS-85 benchmark circuits are presented. The performance pf our GA-based approach is compared with previous results. While the GA generates more efficient input distributions than the previous methods which are based on gradient descent search, the overheads of the GA in computing the input distributions are larger. To account for the relatively quick convergence of the gradient descent methods, we analyze the landscape of the COP-based cost function. We prove that the cost function is unimodal in the search space. This feature makes the cost function amenable to optimization by gradient-descent techniques as compared to random search methods such as Genetic Algorithms.