J. Houston Miller
George Washington University
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Featured researches published by J. Houston Miller.
Combustion and Flame | 1990
Kermit C. Smyth; Paul J. H. Tjossem; Anthony Hamins; J. Houston Miller
Absolute concentration measurements of hydroxyl radical have been made in a laminar, co-flowing methane-air diffusion flame using laser absorption and laser-induced fluorescence methods to probe the A2Σ+ ← X2Π transition. The maximum OH· concentration is found to be 1.8 ± 0.2 × 1016 cm−3 (mole fraction = 5.0 × 10−3) at a temperature of 2080 K, which is twice the value calculated assuming local total equilibrium but less than half that predicted from partial equilibrium (O2 + H2 ⇄ 2OH·). Evidence is presemted that in general partial equilibrium does not exist for the fast, bimolecular chain branching and radical shuffle reactions in this flame. The overall chemical production-destruction rate profile of OH· has been determined, as well as the rates of hydrogen abstraction reactions by hydroxyl radical to form the vinyl and ethynyl radicals. These results are used to identify the most rapid routes for the production of radical species important in chemical growth processes.
Journal of Physical Chemistry A | 2008
Jennifer D. Herdman; J. Houston Miller
Calculations of intermolecular potentials are presented for homo-molecular and hetero-molecular clusters of 24 peri-condensed PAH spanning monomer masses ranging from 78 to 1830 Da. Binding energies of homo-molecular dimers rise rapidly with molecular size and asymptotically approach the experimentally established exfoliation energy for graphite of 5.0 kJ mol(-1) (carbon atom)(-1). Binding energies of hetero-molecular dimers correlate well with the reduced mass of the pair. From calculations of homo-molecular stacks, binding energies were observed to increase with each added molecule and rise asymptotically, approaching a limit which scales linearly with monomer molecular mass. These results are reviewed in the context of molecular growth in flames and in the context of astrophysical observations.
Applied Optics | 1993
J. Houston Miller; Salma Elreedy; Bijan Ahvazi; F. Woldu; P. Hassanzadeh
The application of tunable diode lasers for in situ diagnostics in laminar hydrocarbon diffusion flames is demonstrated. By the use of both direct-absorption and wavelength-modulation (second-derivative) techniques, carbon monoxide concentrations and the local flame temperature are determined for a laminar methane-air diffusion flame supported on a Wolfhard-Parker slot burner. In both cases the results are found to be in excellent agreement with prior measurements of these quantities using bothrobe and optical techniques.
Symposium (International) on Combustion | 1991
J. Houston Miller
A new method is described for the estimation of the rate constants for the agglomeration of Polynuclear Aromatic Hydrocarbons (PAH) in flames. Two models are developed to predict the forward rate of PAH dimerization assuming that (a) the collision energy can be accommodated by the agglomerate or (b) that the energy is removed by collision with a bath gas. Model (a) predicts a rate constant more than 2 times the gas kinetic rate, in good agreement with the reported enhancement due to van der Waals interactions for small particles. The second model leads to rates for agglomeration which are about 5% of the gas kinetic rate, lower by a factor of 4–8 than the sticking coefficients inferred from PAH profiles in flames. The dimerization rate constants are combined with previously determined equilibrium constants for PAH dimerization in a simple model of PAH growth which considers both chemical and physical processes. The results of the model indicate that agglomeration plays only a small role in PAH growth until the dimer lifetimes are long relative to the characteristic time for chemical ring growth. In the prescent calculation, agglomeration becomes important only for collisions of PAH whose mass exceeds ⋍800 amu.
Combustion Science and Technology | 1992
J. Thomas McKinnon; J. Houston Miller
An optical method for monitoring the products of combustion, particularly for the detection of upset conditions in the incineration of hazardous waste, is disclosed. On-line detection of upsets is extremely important to avoid sending untreated waste out the stack plume and to avoid the formation of hazardous products of incomplete combustion, such as dioxins. Small hydrocarbons are the strongest candidates for in situ monitoring of combustion efficiency. The combustion is monitored via infrared absorption using tunable diode lasers (TDLs).
PLOS ONE | 2008
Glauco R. Souza; Esra Yonel-Gumruk; Davin Fan; Jeffrey Easley; Roberto Rangel; Liliana Guzman-Rojas; J. Houston Miller; Wadih Arap; Renata Pasqualini
Hydrogels have become a promising research focus because of their potential for biomedical application. Here we explore the long-range, electrostatic interactions by following the effect of trans-acting (pH) and cis-acting factors (peptide mutation) on the formation of Au-phage hydrogels. These bioinorganic hydrogels can be generated from the bottom-up assembly of Au nanoparticles (Au NP) with either native or mutant bacteriophage (phage) through electrostatic interaction of the phage pVIII major capsid proteins (pVIII). The cis-acting factor consists of a peptide extension displayed on the pVIII that mutates the phage. Our results show that pH can dictate the direct-assembly and stability of Au-phage hydrogels in spite of the differences between the native and the mutant pVIII. The first step in characterizing the interactions of Au NP with phage was to generate a molecular model that identified the charge distribution and structure of the native and mutant pVIII. This model indicated that the mutant peptide extension carried a higher positive charge relative to the native pVIII at all pHs. Next, by monitoring the Au-phage interaction by means of optical microscopy, elastic light scattering, fractal dimension analysis as well as Uv-vis and surface plasmon resonance spectroscopy, we show that the positive charge of the mutant peptide extension favors the opposite charge affinity between the phage and Au NP as the pH is decreased. These results show the versatility of this assembly method, where the stability of these hydrogels can be achieved by either adjusting the pH or by changing the composition of the phage pVIII without the need of phage display libraries.
Combustion and Flame | 1995
R. Reed Skaggs; J. Houston Miller
Abstract Tunable diode laser absorption spectroscopy has been used to map carbon monoxide concentrations and temperatures in a series of laminar ethylene/air, axisymmetric diffusion flames. As the quantity of soot increased, temperatures near the tip of the flames were observed to decrease. Carbon monoxide concentration profiles were found to depend on soot levels with the most dramatic differences apparent along the centerline beyond the stoichiometric surface. These measurements were combined with literature data to calculate oxidation rates for both soot and carbon monoxide. It was found that the oxidation rate for CO low in the flames was larger than that near the visible flame tip, which is attributable to both lower hydroxyl radical concentrations and temperatures at the tip. Further, soot oxidation, which is believed to form CO, occurs at a faster rate than CO oxidation processes at the visible flame tip, thus leading to carbon monoxide emission from the flame.
Combustion Science and Technology | 1990
Anthony Hamins; David T. Anderson; J. Houston Miller
Abstract The concentrations of stable species in an atmospheric-pressure, laminar diffusion flame burning a fuel mixture of methane and toluene (1 mole percent) were measured using a microprobe gas sampling/mass spectrometer system. These measurements are compared to results from a flame burning pure methane under identical temperature and flow conditions. In each of the flames studied little or no change is observed in the peak concentrations of a number of major chemical species such as water, carbon monoxide, and carbon dioxide. Small increases occurred in the peak concentrations of hydrogen, acetylene, methylacetylene, vinylacetylene, diacetylene, and butadiene. The presence of increased amounts of these products suggests limited decomposition of the benzyl or phenyl radicals which are likely initial intermediates of aromatic pyrolysis. Relatively larger increases occurred in the peak concentrations of a number or aromatic compounds including phenylacetylene, styrene, and naphthalene. For the toluene ...
Symposium (International) on Combustion | 1985
J. Houston Miller; Kermit C. Smyth; W. Gary Mallard
Polynuclear aromatic hydrocarbons (PAH) are found in all sooting, hydrocarbon flames. These species are ideally suited to be chemical precursors and building blocks in soot formation, yet their possible role has not been elucidated. From a knowledge of the magnitude of the van der Waals interaction between pairs of PAH the equilibrium constants for dimer formation have been calculated. These values have been used with experimentally measured PAH concentrations to compute dimer concentrations, which were then compared to soot nuclei number densities to determine whether or not the dimers are numerous enough to serve as nucleation sites. The dimers of benzene, coronene (7 rings), and circumcoronene (19 rings), as well as mixed dimer pairs, have been examined. Despite choosing monomer concentrations and theoretical approaches which favor dimer formation, the dimerization of PAH does not yield a sufficient number of nucleation sites to account for soot formation in a homogeneous nucleation mechanism. If PAH do participate in the early stages of soot formation, irreversible chemical steps must be important.
Biomedical Microdevices | 2010
Glauco R. Souza; Fernanda I. Staquicini; Dawn R. Christianson; Michael G. Ozawa; J. Houston Miller; Renata Pasqualini; Wadih Arap
The development of improved methods for targeted cell detection is of general interest in many fields of research and drug development. There are a number of well-established techniques for the study and detection of biomarkers expressed in living cells and tissues. Many of them rely on multi-step procedures that might not meet ideal assay requirements for speed, cost, sensitivity, and specificity. Here we report and further validate an approach that enables spontaneous molecular assembly to generate biologically active networks of bacteriophage (phage) assembled with gold (Au) nanoparticles (termed Au-phage nanoshuttles). Here, the nanoshuttles preserve the cell binding and internalization attributes mediated by a displayed peptide targeted to a cell surface receptor. The organization of such targeted assemblies can be further manipulated to be used as a mutimodal detection assembly, and they can be characterized as fractal nanostructures by angle-dependent light scattering fractal dimension analysis. Targeted Au-phage nanoshuttles offer multiple functionalities for nanotechnology-based sensing and reporting, including enhanced florescence and improved contrast for darkfield microscopy.