Temperature measurements of high-explosive and combustion processes are difficult to obtain due to the speed and environment of the events. To overcome these challenges, we have characterized and calibrated a digital high-speed color camera that may be used to measure the temperature of such events. A two-color ratio method is used to calculate a temperature using the color filter array raw image data and a graybody assumption. If the raw image data are not available, temperatures may be calculated from the processed images or movies, depending on proper analysis of the digital color imaging pipeline. We analyze three transformations within the pipeline (demosaicing, white balance, and gamma correction) to determine their effect on the calculated temperature. Using this technique with a Phantom color camera, we have measured the temperature of exploded C-4 charges. The surface temperature of the resulting fireball was found to rapidly increase after detonation, and subsequently decayed to a constant value of approximately 1980 K.
We present studies of the magnetic field distribution around the vortices in LuNi 2 B 2 C. Small-angle neutron scattering measurements of the vortex lattice ͑VL͒ in this material were extended to unprecedentedly large values of the scattering vector q, obtained both by using high magnetic fields to decrease the VL spacing and by using higher order reflections. A square VL, oriented with the nearest-neighbor direction along the crystalline ͓110͔ direction, was observed up to the highest measured field. The first-order VL form factor, ͉F͑q 10 ͉͒, was found to decrease exponentially with increasing magnetic field. Measurements of the higher-order form factors, ͉F͑q hk ͉͒, reveal a significant in-plane anisotropy and also allow for a real-space reconstruction of the VL field distribution.
[a] 1I ntroductionReactive materials (RM) are as ubset of energetic materials, and include intermetallic or metal/metal oxide (thermite) composites. Although these systems are the most common, the term could be further extended to encompass other composite materials;w hich gives rise to ar apid burst of energy in the form of ap ressure, or thermal pulse. This energy release, combined with the high mass and volumetric energy densities of such materials, makes them attractive candidates for several applications demanding ar apid, and tunable, energy release profile.It has been known for some time that when one reduces the particle size in RM, the apparent reactivity can increase significantly [1].T his has largely been attributed to reduced transport distances between the constituents. However, there are other known features of small particles;w hich could also be af actor;s uch as reduced ignition temperature, activation energy,m elting point, etc. brought forth by the increasing surface to volume ratio. Another property of small, metal particles is that the thin, native oxide shell represents ar elatively larger fraction of the total mass. Several authors have suggested that the reaction mechanism for fine Al particles occurs via diffusional transport of species across this oxide shell [2][3][4][5],w hile others have suggested the large increase in reactivity warrants the need for an ew theory,a nd have speculated that the core-shell interaction under rapid heating can activate am elt dispersion mechanism [6,7].R ecent work has demonstrated that rapid condensed-phase reactions can occur early in the reaction, but it remains unclear to what extent the reaction has completed during this step [8,9].Q uantitative measurements, such as the material burn time, can greatly help improve our fundamental understanding of reaction pathways and mechanisms.Abstract:Acommon method for measuring the reactivity of rapidly deflagrating materials has been to loosely pack ad esired mixture into an approx. 10 cm long 3 mm diameter acrylic tube, ignite the material on one end, and report the observed self-propagating flame velocity through the material. While this method can yield qualitative information, linking this to quantitative intrinsic properties, such as particle burn time, has remained challenging. In this work, we significantly redesign the traditional burn tube experiment. Between 25 and 250 mg of nanocomposite aluminum/copper oxide (Al/CuO) thermite is loosely packed into the capped end of a1 .8 ml ong tube, and the remainder of the tube is left unfilled. The material is ignited using ah ot wire, resulting in as teadily-propagating luminous front, which extends part, or all, of the way down the length of the tube. We suggest the behavior is ar esult of "reactive entrainment", which occurs when the reaction time scale becomes longer than the characteristic momentum relaxation time scale. When this criterion is met, and when there are significant pressure gradients present or produced during the reaction, material will be ...
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