Magnetic gauge measurements on the two-stage gun : homogeneous and heterogeneous initiation of high explosives /

One of the reasons for building our gas-driven two-stage gun at Los Alamos was to be able to do shock initiation experiments on high explosives that were too insensitive to initiate with the single-stage gun. In past ARA meetings we have discussed the operation of the gun and the magnetic gauge measurement method. During the past couple of years we have done a number of magnetic gauge experiments on both liquid and solid high explosives. Shock initiation of high explosives depends on the nature of the material - whether it is homogeneous (liquid) or heterogeneous (pressed solid). In the solid explosives, mostly heterogeneous behavior has been measured. In the liquid explosive isopropyl nitrate, classic homogeneous initiation has been measured including the formation of a superdetonation in the shocked liquid. Experiments in both materials are discussed including the particle (mass) velocity profiles at a number of Lagrangian positions in the flow, progress of the shock front as measured by shock tracker gauges, and the position when the reactive wave reaches a detonation condition. The two-stage gun, in conjunction with the multiple magnetic gauging method, has proven very useful for generating new information in initiation experiments. Information from these experiments is of great value to modelers trying to determine the proper reaction rate models to use in simulations of the shock initiation process

The Sensitivity of Massively Parallel Sequencing for Detecting Candidate Infectious Agents Associated with Human Tissue

Massively parallel sequencing technology now provides the opportunity to sample the transcriptome of a given tissue comprehensively. Transcripts at only a few copies per cell are readily detectable, allowing the discovery of low abundance viral and bacterial transcripts in human tissue samples. Here we describe an approach for mining large sequence data sets for the presence of microbial sequences. Further, we demonstrate the sensitivity of this approach by sequencing human RNA-seq libraries spiked with decreasing amounts of an RNA-virus. At a modest depth of sequencing, viral transcripts can be detected at frequencies less than 1 in 1,000,000. With current sequencing platforms approaching outputs of one billion reads per run, this is a highly sensitive method for detecting putative infectious agents associated with human tissues

Insights into the shock initiation/detonation of homogeneous and heterogeneous HE

It has long been known that there are fundamental differences between homogeneous and heterogeneous high explosives. The shock initiation behavior of these materials was first described in the literature by Campbell et al, in 1961. Chaiken was also involved in describing this process for liquid nitromethane. Since then, there have been a number of studies which have added considerable incite into the shock initiation/detonation behavior of these materials. We only give a few references here (Refs. 4 - 11) and these should be considered representative; e.g. they do not represent an exhaustive list of references available. Many of these studies were done on homogeneous explosives, most often nitromethane (NM) and include particle velocity gauge measurements, optical temperature measurements, VISAR measurements, as well as streak camera measurements of interfaces. In some cases NM was heterogenized by gelling and adding silica particles. Homogeneous materials are typically liquids or single crystals in which there are a minimal number of physical imperfections (e.g. bubbles or voids) that can cause perturbations in the input shock and the flow behind it. Homogeneous materials viewed with macroscopic probes characteristic of detonation physics experiments appear uniform. Heterogeneous explosives are generally all other types; these are usually pressed, cast, machined, or extruded into the shapes or parts desired. These materials contain imperfections of a variety of types that cause fluid-mechanical irregularities (called hot spots) when a shock or detonation wave passes over them. Such hot spots cause associated space/time fluctuations in the thermodynamic fields (e.g., the pressure or temperature fields) in the material. These thermodynamic variations affect the local chemical-heat-release rate - they produce an average heat-release rate that is a combination of chemistry and mechanics. Hot spots could be the result of voids, shock interactions, jetting, shock impedance mismatches, etc. Shock initiation of homogeneous explosives is due to a thermal explosion that occurs in the material shocked the longest. This reaction produces a reactive wave that grows behind the front and eventually overtakes the front. The reactive wave may grow into what is called a superdetonation before it overtakes the initial shock and settles down to a steady detonation. The shock initiation process in heterogeneous explosives differs a great deal because the hot spots cause early chemical reaction as soon as the shock passing over a region creates them. This causes reactive growth both in and behind the shock front. This leads to a relatively smooth growth of the initiating shock to a detonation, in contrast to the abrupt changes that occur in the homogeneous case. These differences are apparent in both the in-situ reaction wave profiles and the acceleration of the shock front

Changes to the LANL gas driven two stage gun : projectile velocity measurement and etc.

stage gun. It was necessary to use optical methods because electrical shorting pins damaged the projectile:, turned .the projectile causing tilted impacts, and sprayed the target with bits of broken pin. The first optical method involved cutting shrzllow grooves in the sides of the projectile at precisely measured intervals. Thc projectile pilssed through a single light beam focused in such a way that the grooves would alternately block and transmit light to a sensing system. This system didn't work because the groovas filled with smoke, blocking the light at all times after the projectile first broke the hearn. The second method used light rcflectetl off the projectile at four different positions. Light from a 400 mW laser was split into four oplical fibers. Half of the light reflected from the end of each B9er 'was retutncd to it phototnulitiplier. When the projectile passed in front of a fiber the amount of returned light increased. This system had a very poor signal to noise ratio: the amount of light returned when the projectile passed in front ofthe fiber was scarcely larger than the noise on the signals. 'I'hc third system used four stations at which laser light was transmitted from one optical fiber to another. 'The projectile passed close by tlhe sending or receiving fiber, rapidly cutting off the transmitted light. This method suffered from a lasix speckle pattern which changed with time thereby giving a constiintly changing inlerisiily. The fiber optic beam splitter used to split the laser light in methods two and three was also very nnstable: the amount of light split into any particular fiber varied with teinperature, vibration, and any movement of fibers. The method which was ultimately successful used it SmW, 670 nni laser diode at each of' four positions. A small lens focused this light to a point through which Ilie projectile passed. Transmitted light was imaged into 700 micron plastic fibers which relayed thhe light to a bank of photomultipliers. 'The combination of imaging the luminous area of the laser diodc and the end of the sensing fiber onto the same plane, through which the projectile passed, piovided veiy good rejection of stray light, a very fast light cutoff as the projectile passed tlwough the focal point, and efficient use of light. Projectile velocities were measured with an accuracy of 1 part in 1,000. In addition to our optical projectile velocity measuring system, we have significantly changed our projectiles, OUI transition section diaphragms, and developed a new honing teditiique. Thesc will be briefly discuswd as well

The Politics of Sociotechnical Intervention: An Interactionist View

In this article, we apply concepts from symbolic interactionism - a well-established tradition of interpretivist sociology - to investigate the social and political processes involved in a sociotechnical intervention. The intervention was designed to elicit operator involvement in an experimental trial of an advanced manufacturing system at an industrial site in Australia. The interactionist concepts of social worlds, boundary objects and trajectories are used to explore the interrelationships among the theoretical, practical and contextual elements of intervention. We believe that these concepts are flexible intellectual resources that can extend and enrich our understanding of the politics involved in the shaping of work and technology. Such an understanding is necessary if the fields of user participation and sociotechnical design are to move beyond the production of normative discourses and methods into effective interventions in the complex social environments in which technical decisions are made

Particle velocity measurements of the reaction zone in nitromethane

The detonation reaction-zone length in neat, deuterated, and chemically sensitized nitromethane (NM) has been measured by using several different laser-based velocity interferometry systems. The experiments involved measuring the particle velocity history at a NM/PMMA (polymethylmethacrylate) window interface during the time a detonation in the NM interacted with the interface. Initially, Fabry-Perot interferometry was used, but, because of low time resolution (>5 ns), several different configurations of VISAR interferometry were subsequently used. Early work was done with VISARs with a time resolution of about 3 ns. By making changes to the recording system, we were able to improve this to {approx}1 ns. Profiles measured at the NM/PMMA interface agree with the ZND theory, in that a spike ({approx}2.45 mm/{micro}s) is measured that is consistent with an extrapolated reactant NM Hugoniot matched to the PMMA window. The spike is rather sharp, followed by a rapid drop in particle velocity over a time of 5 to 10 ns; this is evidence of early fast reactions. Over about 50 ns, a much slower particle velocity decrease occurs to the assumed CJ condition - indicating a total reaction zone length of {approx}300 {micro}m. When the NM is chemically changed, such as replacing the hydrogen atoms with deuterium or chemically sensitizing with a base, some changes are observed in the early part of the reaction zone

Circos [16]plot detailing HaRNAV sequence recovery.

<p>The red and blue lines represent reads aligning on the minus and plus strand, respectively. The Heterosigma akashiwo RNA virus has an 8,587 bp ss-RNA linear genome with a single CDS, shown in green on the circos plot. The read depth of coverage is shown in the centre of the plot. The genome is depicted by alternating black-white arcs of 500 bp in size.</p