An Editorial Comment

Recommendations for change in increased access and equity in education of African-American individuals: What do we do while we wait

Reproducibility Distinguishability and Correlation of Fireball and Shockwave Dynamics in Explosive Munitions Detonations

The classification of battlespace detonations, specifically the determination of munitions type and size using temporal and spectral features of infrared emissions, is a particularly challenging problem. The intense infrared radiation produced by the detonation of high explosives is largely unstudied. Furthermore, the time-varying fireball imagery and spectra are driven by many factors including the type, size and age of the chemical explosive, method of detonation, interaction with the environment, and the casing used to enclose the explosive. To distinguish between conventional military munitions and improvised or enhanced explosives, the current study investigates fireball expansion dynamics using high speed, multi-band imagery. Instruments were deployed to three field tests involving improvised explosives in howitzer shells, simulated surface-to-air missiles, and small caliber muzzle flashes. The rate of shockwave expansion for the improvised explosives was determined from apparent index of refraction variations in the visible imagery. Fits of the data to existing drag and explosive models found in the literature, as well as modifications to these models, showed agreement in the near- and mid-fields (correlation coefficient, r2 \u3e 0.985 for t \u3c 50 msec); the modified models typically predicted the time for the shockwave to arrive a kilometer away to better than 10%; and fit parameters typically had an uncertainty of less than 20%. The shockwave was distinctive (Fisher Ratio, FR \u3e 1) within the first 2-10 milliseconds after detonation, then it decayed to an indistinguishable acoustic wave (coefficient of variation, CV \u3c 0.05). The area profiles of the fireballs were also examined and found to be highly variable, especially after 10 milliseconds (CV \u3e 0.5), regardless of munitions type. Scaling relationships between properties of the explosive (mass, specific energies, and theoretical energies) and detonation areas, characteristic times, and properties of the shockwave were assessed for distinguishing weights and types: Efficiency decreased with mass (FR \u3e 19); early-time Mach number and overpressure were primarily dependent on energy release (FR ~ 1.5-10); fireball area increased cubically with specific energies (r2 ~ 0.3-0.76) but its time of occurrence decreased cubically (r2 ~ 0.4-0.67). The relationship between fireball and shockwave features was fairly independent of variability (r2 ~ 0.5-0.9), indicating that both fireball and shockwave features scale similarly with variability in detonations

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Table of contents and editorial information for Vol. 18, no. 1, Fall 1990

Table of contents and editorial information for this special issue The Academic Success of African-American Students

An Overview of this Issue

This special issue addresses theoretical, institutional, student and family issues that significantly impact the academic success of African-American students today

Educational Considerations, vol. 18 (1) Full Issue

Educational Considerations, vol. 18 (1) Fall 1990 - Full issu

Characterization and Discrimination of Large Caliber Gun Blast and Flash Signatures

Two hundred and one firings of three 152 mm howitzer munitions were observed to characterize firing signatures of a large caliber gun. Muzzle blast expansion was observed with high-speed (1600 Hz) optical imagery. The trajectory of the blast front was well approximated by a modified point-blast model described by constant rate of energy deposition. Visible and near-infrared (450 - 850 nm) spectra of secondary combustion were acquired at 0.75 nm spectral resolution and depict strong contaminant emissions including Li, Na, K, Cu, and Ca. The O2 (X-b) absorption band is evident in the blue wing of the potassium D lines and was used for monocular passive ranging accurate to within 4 - 9%. Time-resolved midwave infrared (1800 - 6000 cm-1) spectra were collected at 100 Hz and 32 cm-1 resolution. A low dimensional radiative transfer model was used to characterize plume emissions in terms of area, temperature, soot emissivity, and species concentrations. Combustion emissions have 100 ms duration, 1200 - 1600 K temperature, and are dominated by H2O and CO2. Noncombusting plume emissions last 20 ms, are 850 - 1050 K, and show significant continuum (emissivity 0.36) and CO structure. Munitions were discriminated with 92 - 96% classification accuracy using only 1 - 3 firing signature features

Study of cryogenic propellant systems for loading the space shuttle

Computer programs were written to model the liquid oxygen loading system for the space shuttle. The programs allow selection of input data through graphic displays which schematically depict the part of the system being modeled. The computed output is also displayed in the form of graphs and printed messages. Any one of six computation options may be selected. The first four of these pertain to thermal stresses, pressure surges, cooldown times, flow rates and pressures during cooldown. Options five and six deal with possible water hammer effects due to closing of valves, steady flow and transient response to changes in operating conditions after cooldown. Procedures are given for operation of the graphic display unit and minicomputer