Jeffrey B. Morris

The development of a quantitative structure property relationship (QSPR) for the prediction of dielectric constants using neural networks

Abstract The use of quantitative structure property relationships (QSPRs) is proposed for the calculation of dielectric constants. A data set of 497 compounds with a wide variety of functional groups is assembled. These compounds span the dielectric constant range 1–40. A total of 65 molecular descriptors is calculated for these compounds. These descriptors include the dipole moment, polarizability, counts of elemental types, an indicator of hydrogen bonding capability, charged partial surface area descriptors, and molecular connectivity descriptors. Subsets of these descriptors are used to build models in an attempt to find the best possible correlation between chemical structure and dielectric constant. A total of 70 000 models are examined. Neural networks using the Broyden–Fletcher–Goldfarb–Shanno (BFGS) training algorithm are employed to build the models. A total of 191 models have test set errors less than 2.0 and training set errors less than 3.0, where the errors are calculated as the mean of the absolute values of the residuals for sets of 97 and 350 compounds, respectively.

Tomographic analysis of CO absorption in a low-pressure flame.

Tomographic analysis is used to provide a correction to low-pressure stoichiometric premixed CH(4)/O(2) flame temperatures measured with tunable diode laser absorption spectroscopy employing CO two-line thermometry. It is shown that flame temperatures measured with line-of-sight-based two-line thermometry are always too low and that the correction to the observed temperature is a nonlinear function of the height above the burner surface. It is also shown that, at a given height in the flame, a constant temperature across the flame does not imply that vibrational populations are constant and that, at low pressures (<20 Torr), the flame spreads radially beyond the burner diameter and so may no longer be approximated by a one-dimensional model.

Improved quantitative structure property relationships for the prediction of dielectric constants for a set of diverse compounds by subsetting of the data set

In a recent publication we explored the development of quantitative structure property relationships for the calculation of dielectric constants, which resulted in a general model for a wide range of compounds. Our current work explores the division of the set of compounds into eight more homogeneous subsets for which local models are developed. The full data set consists of 454 compounds with dielectric constants ranging from 1 to 40. A pool of up to 16 molecular descriptors is calculated for each of the eight data sets. The descriptors include dipole moment, polarizability, counts of elemental types or functional groups, charged partial surface area, and molecular connectivity. All possible 4-16 descriptor models are calculated for each of the eight data sets, and the best models are selected and compared to the results obtained from the best general model for all 454 compounds. Neural networks using the Broyden-Fletcher-Goldfarb-Shanno training algorithm are employed to build the models. The resulting combined mean test set error for the eight local models of 1.31 is significantly better than the mean test set error of 1.85 for the general model.

Solubility and phase behavior of PEP binders in supercritical carbon dioxide

Abstract Solubility and phase behavior data to temperatures of 300°C and pressures to 3000 bar are presented for various propellant, explosive, and pyrotechnic (PEP) binder polymers in supercritical (SC) carbon dioxide (CO 2 ) with and without modifiers. The binder polymers investigated in this study are polyethylene (PE), oxidized PE, poly(urethane), cellulose acetate butyrate (CAB), poly(vinylidene fluoride-co-hexafluoropropylene) with ∼20mol% hexafluoropropylene (Fluorel™ and Viton™), and poly(chlorotrifluoroethylene-co-vinylidene fluoride) with 24 mol% (Kel-F™ 800) and 69 mol% (Kel-F™ 3700) vinlyidene fluoride. CO 2 has the characteristics of a weak polar solvent which does not dissolve polyethylene although it is can dissolve low molecular weight nonpolar waxes. However, CO 2 is not polar enough to dissolve very polar polymers, such as oxidized PE, polyurethane, Kel-F™ 3700, and CAB. Moderately polar poly(vinylidene fluoride-co-hexafluoropropylene), which is a partially fluorinated polyolefin, and Kel-F™ 800 are soluble in CO 2 due to the polar contributions of the vinylidene fluoride repeat units. The solubility of these two copolymers can be further enhanced using acetone as a modifier with CO 2 . Additionally, oxidized PE is soluble in CO 2 with acetone and ethanol as modifiers, but temperatures greater than ∼200°C are needed. The fact that many of these polymers are soluble in neat CO 2 suggests the potential for a substantial impact upon environmentally sound processing technologies for polymer-based PEP materials.

Laser initiation thresholds of a 'green' aluminum/molybdenum-trioxide metastable intermolecular composite and other pyrotechnics

Metastable intermolecular composites (MIC) consisting of nanometer-scale aluminum and molybdenum trioxide have been proposed as fast initiators. A compound of this class of material was evaluated as a potential environmentally friendly replacement pyrotechnic material for lead styphnate for use in the primer of the M230 medium-caliber automatic cannon. In addition to removing the lead hazard, laser ignition would also reduce or remove certain hazards due to electrostatic or radio frequency radiation. This study was conducted with both a flashlamp-pumped Nd+3:YAG laser and a fiber-coupled diode laser. The measured threshold ignition energies of the MIC and two other inorganic pyrotechnic compounds are presented. The low ignition threshold, advances in diode laser technology, and compact size of the diode laser indicated that laser diode technology could be an ideal candidate ignition source for the M230 cannon. The candidate pyrotechnic compounds were also evaluated for suitability in laser initiation via measurement of time-to-first-light. This metric provided a measurement of the potential for achievement of the necessary action time required for proper cannon operation.

Approximate techniques for the calculation of heats of explosion using thermochemical computer codes

Abstract Procedures are outlined for calculating the heats of explosion (HEX) of neat energetic materials or propellant/explosive formulations using thermochemical computer codes. The “exact” method and three approximate techniques are described; the approximate techniques either eliminate the need to sum the internal energies of the predicted products, or eliminate the need to specify a freeze-out temperature. The various techniques are illustrated for HMX and a nitrocellulose/nitroglycerine (NC/NG) mixture.

FT-Raman Spectroscopy of Some Energetic Materials and Propellant Formulations

Fourier transform Raman (FTR) spectroscopy employing near-IR laser radiation at 1.06 microns as the scattering source is used to obtain Raman spectra of some pure energetic materials and some propellant formulations containing those energetic materials. It is shown that FTR spectroscopy is a useful tool in determining the principle crystalline ingredient in many non-colored propellant formulations.

Achrotech: achromat cost versus performance for conventional, diffractive, and GRIN components

An achromatic component shares a common focus at two wavelengths and is a commonly used device in optical assemblies. This work explores the cost versus performance tradeoff for several types of achromatic lenses: conventional doublets with homogenous glass elements, hybrid doublets with a diffractive surface, axial GRadient INdex (GRIN) lenses (where the index of refraction changes along the length of the lens), and radial GRIN lenses (where the index of refraction changes depending on radial position). First order achromatic principles will be reviewed and applied to each system as a starting point and refined through the use of ray trace software. Optical performance will be assessed in terms of focusing efficiency and imaging. Cost will then be evaluated by accounting for current manufacturing costs and retail price through several distributors.

Comparative infrared and Raman spectroscopy of compounds in high-pressure media

The techniques of Fourier transform infrared spectroscopy (FT-IR) and Fourier transform Raman spectroscopy (FT-R) are compared for use in high pressure environments such as those encountered when using supercritical fluid solvents. FT-IR spectra in the 1000 to 3000 cm-1 region show severe pressure broadening of high-pressure molecular solvents, which eliminates much of the useful spectral range when using this technique. These solvent interferences are not a problem with FT-R at pressures as high as 35 MPa. Spectra of naphthalene in liquid carbon dioxide are used to compare these two spectroscopic techniques.