Room-temperature gas sensors based on gallium nitride nanoparticles

Room-temperature sensing characteristics for H-2, ethanol, NH3, H2S and water have been investigated with thick-film sensors based on GaN nanoparticles, prepared by a simple chemical route. In general, GaN nanoparticles exhibit satisfactory sensor properties for these gases and vapors even at room temperature. The sensitivity for ethanol is found to be highest, the sensitivity and recovery times being smallest. Gas sensor properties of GaN seem to be related to intrinsic defects, which act as sorption sites for the gas molecules. (c) 2010 Elsevier Ltd. All rights reserved.

Sonochemical synthesis of Ce1-xFexO2-delta (0 <= x <= 0.45) and Ce0.65Fe0.33Pd0.02O2-delta nanocrystallites: oxygen storage material, CO oxidation and water gas shift catalyst

Nanocrystalline Ce1-xFexO2-delta (0 <= x <= 0.45) and Ce0.65Fe0.33Pd0.02O2-delta of similar to 4 nm sizes were synthesized by a sonochemical method using diethyletriamine (DETA) as a complexing agent. Compounds were characterized by powder X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and transmission electron microscopy (TEM). Ce1-xFexO2-delta (0 <= x <= 0.45) and Ce0.65Fe0.33Pd0.02O2-delta crystallize in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe3+ ion in CeO2, lattice oxygen is activated and 33% Fe substituted CeO2 i.e. Ce0.67Fe0.33O1.835 reversibly releases 0.31O] up to 600 degrees C which is higher or comparable to the oxygen storage capacity of CeO2-ZrO2 based solid solutions (Catal. Today 2002, 74, 225-234). Due to interaction of redox potentials of Pd2+/0(0.89 V) and Fe3+/2+ (0.77 V) with Ce4+/3+ (1.61 V), Pd ion accelerates the electron transfer from Fe2+ to Ce4+ in Ce0.65Fe0.33Pd0.02O1.815, making it a high oxygen storage material as well as a highly active catalyst for CO oxidation and water gas shift reaction. The activation energy for CO oxidation with Ce0.65Fe0.33Pd0.02O1.815 is found to be as low as 38 kJ mol(-1). Ce0.67Fe0.33O1.835 and Ce0.65Fe0.33Pd0.02O1.815 have also shown high activity for the water gas shift reaction. CO conversion to CO2 is 100% H-2 specific with these catalysts and conversion rate was found to be as high 27.2 mu moles g(-1) s(-1) and the activation energy was found to be 46.4 kJ mol(-1) for Ce0.65Fe0.33Pd0.02O1.815.

Mixed Convection Induced in a Gas Flowing Past a Hot Horizontal Flat Plate

A boundary layer analysis of mixed convective motion over a hot horizontal flat plate is performed under the conditions of steady flow and low speed. Use of the Howarth-Dorodnytsyn transformation makes it possible to dispense with the usual Boussinesq approximation, and variable gas properties are accounted for via the assumption that dynamic viscosity and thermal conductivity are proportional to the absolute temperature. The formulation presented enables the entire mixed convection regime to be described by a single set of equations. Finite difference solutions when the Prandtl number is 0.72 are obtained over the entire range of the mixed convection parameter ξ from 0 (free convection) to 1 (forced convection) and heating parameter ▵ values from 2 to 12. The effects of both ξ and ▵on the velocity profiles, the temperature profiles, and the variation of skin friction and heat transfer functions are clearly illustrated in tables and graphs.

The short range interactions between two rare gas atoms

The short range interactions in He2, Ne2 and Ar2 have been studied in terms of the electronic forces as functions of their internuclear separations employing their single configuration SCF wave functions. The results show that the constituent molecular orbitals behave differently in terms of the forces they exert on the nuclei during the interaction process. The different behaviour of the orbitals is also reflected in the redistribution of charges.

Experimental evaluation of the aeroacoustic characteristics of a source of pulsating gas flow

Amongv arioums ethodtsh,e t ransmissliionne o r thei mpedantcueb em ethohda sb eenm ospt opulafro r thee xperimenetavla luatioonf thea cousticiaml pedanocef a terminatioTnh. ee xistinmg ethodisn,c luding theo nesre porteeda rlierb, y thea uthorrse quirleo catioonf thes oundp ressumrei nima nd/orm axima, or elsem akeu se0 f somei terativep rocedureTsh. e presenpt aperd ealsw ith a methodo f analysios f standinwga vews hichd oesn otd epenodn anyo f thesein volvepdr ocedureIts i.s applicabtloe thec aseo f stationarays w ella sm ovingm ediaI.t enableosn to evaluatteh e impedancoef anyp assivbel ackb ox,a s well as the aeroacoustcich aracteristicosf a sourceo f pulsatingg asf low, with the leaste xperimentawl ork andc omputatiotinm ea ndw itht hee xtraa dvantagoef usinga givenim pedanctueb ef or wavelengtahss largea s fourt imesit s lengthA. methodo f externaml easuremenntost, involvinugs eo f anyi mpedance tubef, or evaluatintgh ea eroacouscthica racteristoicf as sourcoef pulsatingga sf lowi s alsod ealtw ith, based on the definition of attenuation or insertion loss of a muffler.

Cross-field gas breakdown in a coaxial cylinder geometry

Sparking potentials in a coaxial cylinder geometry in oxygen and dry air were measured in crossed electric and magnetic fields. From the data effective collision frequencies were calculated using the equivalent pressure concept. It is shown that the equivalent pressure concept holds good for deriving the effective collision frequencies in non-uniform electric fields.

Novel kinetic scheme for the ammonium perchlorate gas phase

A novel gas-phase kinetic scheme for ammonium perchlorate (AP) deflagration involving 22 reactions among 18 species is developed. The kinetic scheme is based on a study of the effect of initial conditions on the solution of the differential equations of adiabatic constant-pressure combustion kinetics. The existence of condensed-phase reaction products providesalternate pathways for the consumption of NH3 and HCIOl produced by gas-phase dissociation of AP. Theoretically obtained temperature-time profiles of the novel scheme do not change when the conventional reaction pathways are included, indicatingthat the novel scheme is a substantially faster rate process. The new scheme does not involve the species CIO, which has long been considered a critical component of the AP gas phase and which is included in the conventional reaction pathways.The new scheme develops faster overall reaction rates, steeper temperature-time profiles, and in a deflagration model will result in higher heat-transfer rates from gas phase to the condensed phase.

Design and fabrication of an automated thermal desorption gas-solid reaction system: Oxidation of ammonia and methanol over YBa2Cu3O7−δ(123) oxide systems

A fully automated, versatile Temperature Programmed Desorption (TDP), Temperature Programmed Reaction (TPR) and Evolved Gas Analysis (EGA) system has been designed and fabricated. The system consists of a micro-reactor which can be evacuated to 10−6 torr and can be heated from 30 to 750°C at a rate of 5 to 30°C per minute. The gas evolved from the reactor is analysed by a quadrupole mass spectrometer (1–300 amu). Data on each of the mass scans and the temperature at a given time are acquired by a PC/AT system to generate thermograms. The functioning of the system is exemplified by the temperature programmed desorption (TPD) of oxygen from YBa2Cu3−xCoxO7 ± δ, catalytic ammonia oxidation to NO over YBa2Cu3O7−δ and anaerobic oxidation of methanol to CO2, CO and H2O over YBa2Cu3O7−δ (Y123) and PrBa2Cu3O7−δ (Pr123) systems.

Estimating national contributions of greenhouse gas emissions :The CSE-WRI controversy

Analysts have identified four related questions that need to be asked and answered before agreements to respond to global warming will be possible.1 Which countries bear responsibility for causing the problem? What quantities and mix of greenhouse gases should each country be allowed to emit? Which countries have the resources to do something about the problem? Where are the best opportunities for undertaking projects to respond to the problem? Failure to distinguish among these four questions, or willingness to accept superficial answers, promotes unnecessary controversy.

Gradient solid-electrolyte for use with dissimilar gas electrodes

The EMF of a solid-state cell, incorporating a composite solid-electrolyte with gradual variation in composition, and dissimilar gas electrodes, has been studied as a function of temperature and partial pressures at the electrodes. The cell with the configuration: Pt, CO2' + O2' parallel-to Na2CO3\Na(SO4)x(CO3)1-x\Na2SO4 parallel-to SO3'' + SO2'' + O2'', Pt x=0 x=1 was investigated in the temperature range 973 to 1079 K. The solid-electrolyte surface exposed to SO3 + SO2 + O2 gas mixture was doped-Na2SO4, whereas the CO2 + O2 gas mixture was in contact with pure Na2CO3. The composition of the solid solution between the carbonate and sulfate, with hexagonal structure, was varied gradually between the boundary values. It has been found that the EMF of the cell is close to that calculated from thermodynamic data, assuming unit transport number for Na+ ions. The gradient in the concentration of sulfate and carbonate ions in the electrolyte does not give rise to a significant diffusion potential.

Accretion of Chaplygin gas upon black holes: formation of faster outflowing winds

We study the accretion of modified Chaplygin gas upon different types of black holes. Modified Chaplygin gas is one of the best candidates for a combined model of dark matter and dark energy. In addition, from a field theoretical point of view the modified Chaplygin gas model is equivalent to that of a scalar field having a self-interacting potential. We formulate the equations related to both spherical accretion and disc accretion, and respective winds. The corresponding numerical solutions of the flow, particularly of velocity, are presented and analysed. We show that the accretion-wind system of modified Chaplygin gas dramatically alters the wind solutions, producing faster winds, upon changes in physical parameters, while accretion solutions qualitatively remain unaffected. This implies that modified Chaplygin gas is more prone to produce outflow which is the natural consequence of the dark energy into the system.

Digital simulation of galvanostatic current-potential data for gas-diffusion electrodes and estimation of electrodekinetic parameters

A computerized non-linear-least-squares regression procedure to analyse the galvanostatic current-potential data for kinetically hindered reactions on porous gas-diffusion electrodes is reported. The simulated data fit well with the corresponding measured values. The analytical estimates of electrode-kinetic parameters and uncompensated resistance are found to be in good agreement with their respective values obtained from Tafel plots and the current-interrupter method. The procedure circumvents the need to collect the data in the limiting-current region where the polarization values are usually prone to errors. The polarization data for two typical cases, namely, methanol oxidation on a carbon-supported platinum-tin electrode and oxygen reduction on a Nafion-coated platinized carbon electrode, are successfully analysed.

Exact Solution of a One-Dimensional Multicomponent Lattice Gas with Hyperbolic Interaction

We present the exact solution to a one-dimensional multicomponent quantum lattice model interacting by an exchange operator which falls off as the inverse sinh square of the distance. This interaction contains a variable range as a parameter and can thus interpolate between the known solutions for the nearest-neighbor chain and the inverse-square chain. The energy, susceptibility, charge stiffness, and the dispersion relations for low-lying excitations are explicitly calculated for the absolute ground state, as a function of both the range of the interaction and the number of species of fermions.

PVU and wave-particle splitting schemes for Euler equations of gas dynamics

A new way of flux-splitting, termed as the wave-particle splitting is presented for developing upwind methods for solving Euler equations of gas dynamics. Based on this splitting, two new upwind methods termed as Acoustic Flux Vector Splitting (AFVS) and Acoustic Flux Difference Splitting (AFDS) methods are developed. A new Boltzmann scheme, which closely resembles the wave-particle splitting, is developed using the kinetic theory of gases. This method, termed as Peculiar Velocity based Upwind (PVU) method, uses the concept of peculiar velocity for upwinding. A special feature of all these methods that the unidirectional and multidirectional parts of the flux vector are treated separately. Extensive computations done using these schemes demonstrate the soundness of the ideas.