Chethan K. Gaddam

Quantification of nano-scale carbon structure by HRTEM and lattice fringe analysis

Image processing is applied to extract material structure on the nanometer scale.Output statistics are shown to be insensitive to processing parameters.The image analysis algorithm is robust for diversity of nanoscale structure.Solid-state transformation is demonstrated for e-beam irradiated polyhedral carbon. An image analysis algorithm is applied to materials for characterization of solid-state structure on a nanometer scale using model carbon materials. Nanoscale carbons in the form of soots offer ease of demonstration while being relevant to human health and climate concerns. Demonstrated here is an image analysis algorithm applied to three nanoscaled carbon materials: a disordered soot, and two highly ordered soots featuring flat or curved atomic layer planes. Nanostructure parameters consisting of graphene layers length and tortuosity are extracted from high-resolution transmission electron microscopy images. The algorithm is composed of two major parts: (a) image processing that generates a skeletonized binary image, and (b) characterization that generates statistics on length and tortuosity based on the skeletonized image of the graphene layers. Algorithm robustness for variations in image processing parameters of contrast and threshold is demonstrated by similarity of output distributions of disordered diesel engine produced soot. Algorithm processing range was illustrated using highly ordered soots with flat (graphitic) and curved lattice nanostructure. Time resolved image analysis of an image sequence for polyhedral onions under electron irradiation demonstrate algorithm utility for tracking solid-state transformations. Display Omitted

An investigation of micro-hollow cathode glow discharge generated optical emission spectroscopy for hydrocarbon detection and differentiation.

The analytical utility of a micro-hollow cathode glow discharge plasma for detection of varied hydrocarbons was tested using acetone, ethanol, heptane, nitrobenzene, and toluene. Differences in fragmentation pathways, reflecting parent compound molecular structure, led to differences in optical emission patterns that can then potentially serve as signatures for the species of interest. Spectral simulations were performed emphasizing the CH (A2Δ–X2Π), CH (C2∑–X2Π), and OH (A2∑+–X2Π) electronic systems. The analytical utility of selected emission lines is demonstrated by a linear relationship between optical emission spectroscopy and parent compound concentration over a wide range, with detection limits extending down to parts per billion (ppb) levels.

A Laboratory Comparison of Emission Factors, Number Size Distributions, and Morphology of Ultrafine Particles from 11 Different Household Cookstove-Fuel Systems

Ultrafine particle (UFP) emissions and particle number size distributions (PNSD) are critical in the evaluation of air pollution impacts; however, data on UFP number emissions from cookstoves, which are a major source of many pollutants, are limited. In this study, 11 fuel-stove combinations covering a variety of fuels and different stoves are investigated for UFP emissions and PNSD. The combustion of LPG and alcohol (∼1011 particles per useful energy delivered, particles/MJd), and kerosene (∼1013 particles/MJd), produced emissions that were lower by 2-3 orders of magnitude than solid fuels (1014-1015 particles/MJd). Three different PNSD types-unimodal distributions with peaks ∼30-40 nm, unimodal distributions with peaks <30 nm, and bimodal distributions-were observed as the result of both fuel and stove effects. The fractions of particles smaller than 30 nm (F30) varied among the tested systems, ranging from 13% to 88%. The burning of LPG and alcohol had the lowest PM2.5 mass emissions, UFP number emissions, and F30 (13-21% for LPG and 35-41% for alcohol). Emissions of PM2.5 and UFP from kerosene were also low compared with solid fuel burning but had a relatively high F30 value of approximately 73-80%.

Spectroscopic characterization and comparison between biologics, organics and mineral compounds using pulsed micro-hollow glow discharge

A new mode of operation – pulsed – is demonstrated for compound identification of solid materials in the form of dry powders. Both plasma and analytical utility are characterized spectroscopically. The acquired emission spectra provided molecular and elemental information. The microgram sample analysis capability and atmospheric pressure operation are demonstrated for benign and biological organics, a commercial fertilizer and other inorganic materials. The plasma temperature is estimated by spectral simulation of the NO (A2Σ+ → X2Π) bands, and the inferred temperature is 1300 °C. Atomic transitions from C (1P0 → 1S) and molecular bands from CH (B2Σ → X2Π) and CH (A2Δ → X2Π) were manifestly observed in the optical emission spectra of organic materials. Relative intensities of common spectral signatures could distinguish biological agents from common benign organic materials. High-resolution spectra were particularly useful in resolving and identifying atomic transitions such as Mg, Ca, Fe and Si for the inorganic materials. Such a detector system has the capability to rapidly sense hazards with the added advantage of portability.

Atmospheric Microplasma Jet: Spectroscopic Database Development and Analytical Results

This paper presents a developed dielectric-barrier-discharge-based “sniffer” that offers unique characteristics not available from other techniques. It is a portable, highly specific, and sensitive detector that operates at atmospheric pressure. It provides both molecular and elemental information on organic and inorganic gases and particulate aerosols. Measurements were made to electrically characterize the plasma and calculate the energy coupled into the plasma. We created a signature database for diverse chemicals based on the atomic and diatomic emission spectrum that serves to classify the compound and ideally recognize it by composition with the optical emission intensity corresponding to concentration. For some operational regimes and species, emission from OH (A2Σ+-X2π), CH (A2Δ-X2π), and often C2 (d3πg-a3πu; Swan band system) diatomic radicals is produced. Limits of detection extend to parts per billion (ppb) levels for some species such as decane, 2-decanol, and nitrobenzene. Results are presented for differentiation of classes of organic compounds such as alkanes, aromatics, oxygenates, chlorinated, and nitrogen-containing organic compounds.