Characterization of PAX‐21 Insensitive Munition Detonation Residues

Insensitive high explosives are being used in military munitions to counteract unintended detonations during storage and transportation. These formulations contain compounds such as 2,4‐dinitroanisole (DNAN) and 3‐nitro‐1,2,4‐triazol‐5‐one (NTO), which are less sensitive to shock and heat than conventional explosives. We conducted a series of four tests on snow‐covered ice utilizing 60‐mm mortar cartridges filled with 358 g of PAX‐21, a mixture of RDX, DNAN, and ammonium perchlorate. Rounds were detonated high‐ and low‐order using a fuze simulator to initiate detonation. Blow‐in‐place (BIP) operations were conducted on fuzed rounds using an external donor charge or a shaped‐charge initiator. Results indicate that 0.001 % of the original mass of RDX and DNAN were deposited during high‐order detonations, but up to 28 % of the perchlorate remained. For the donor block BIPs, 1 % of the RDX and DNAN remained. Residues masses for these operations were significantly higher than for conventional munitions. Low‐order detonations deposited 10–15 % of their original explosive filler in friable chunks up to 5.2 g in mass. Shaped‐charge BIPs scattered 15 % of the filler and produced chunks up to 15 g. Ammonium perchlorate residue masses were extremely high because of the presence of large AP crystals, up to 400 μm in the recovered particles.     

Electrochemical Corrosion Behaviour of 90—10 Cu—Ni Alloy in Chloride-Based Electrolytes

The corrosion of 90–10 copper—nickel alloy in aqueous chloride electrolytes has received considerable attention in the literature due to its widespread use in seawater and saline environments. From an analysis of the electrochemical behaviour of the alloy, it is clear that both the polarization and mixed/corrosion potential characteristics show a close comparison to unalloyed copper. Important differences arise, however, due to the semi—conducting nature, composition and overall protectiveness of the corrosion products on the 90–10 copper—nickel alloy. In this work the metallurgy, electrochemistry and mechanism of passivation of the alloy are reviewed to provide a focused source of data regarding the electrochemical characteristics of the alloy in saline media.     

Involvement of surface cysteines in activity and multimer formation of thimet oligopeptidase

Thimet oligopeptidase is a metalloenzyme involved in regulatingneuropeptide processing. Three cysteine residues (246, 248,253) are known to be involved in thiol activation of the enzyme.In contrast to the wild-type enzyme, the triple mutant (C246S/C248S/C253S)displays increased activity in the absence of dithiothreitol.Dimers, purportedly formed through cysteines 246, 248 and 253,have been thought to be inactive. However, analysis of the triplemutant by native gel electrophoresis reveals the existence ofdimers and multimers, implying that oligomer formation is mediatedby other cysteines, probably on the surface, and that some ofthese forms are enzymatically active. Isolation and characterizationof iodoacetate-modified monomers and dimers of the triple mutantrevealed that, indeed, certain dimeric forms of the enzyme arestill fully active, whereas others show reduced activity. Cysteineresidues potentially involved in dimerization were identifiedby modeling of thimet oliogopeptidase to its homolog, neurolysin.Five mutants were constructed; all contained the triple mutationC246S/C248S/C253S and additional substitutions. Substitutionsat C46 or C682 and C687 prevented multimer formation and inhibiteddimer formation. The C46S mutant had enzymatic activity comparableto the parent triple mutant, whereas that of C682S/C687S wasreduced. Thus, the location of intermolecular disulfide bonds,rather than their existence per se, is relevant to activity.Dimerization close to the N-terminus is detrimental to activity,whereas dimerization near the C-terminus has little effect.Altering disulfide bond formation is a potential regulatoryfactor in the cell owing to the varying oxidation states insubcellular compartments and the different compartmental locationsand functions of the enzyme. Received March 1, 2003; revised June 17, 2003; accepted June 23, 2003.     

Flow influenced electrochemical corrosion of nickel aluminium bronze – Part I. Cathodic polarisation

The cathodic polarisation behaviour of CA 104 nickel aluminium bronze (NAB) has been examined in fully characterised seawaters (filtered and artificial) using the rotating disc electrode (RDE) and the rotating cylinder electrode (RCE). Linear sweep voltammetry and a potential step, current transient technique were used to examine the charge transfer and mass transfer controlled cathodic response as a function of both laminar and turbulent fluid flow. For freshly polished surfaces, the rate of irreversible charge transfer controlled oxygen reduction is controlled by the exchange of a single electron and hydrogen evolution is only significant at potentials more negative than approximately –1.0 V vs. the saturated calomel electrode (SCE).     

Non-heme Fe(IV)-oxo intermediates

High-valent non-heme iron-oxo intermediates have been proposed for decades as the key intermediates in numerous biological oxidation reactions. In the past three years, the first direct characterization of such intermediates has been provided by studies of several alphaKG-dependent oxygenases that catalyze either hydroxylation or halogenation of their substrates. In each case, the Fe(IV)-oxo intermediate is implicated in cleavage of the aliphatic C-H bond to initiate hydroxylation or halogenation. The observation of non-heme Fe(IV)-oxo intermediates and Fe(II)-containing product(s) complexes with almost identical spectroscopic parameters in the reactions of two distantly related alphaKG-dependent hydroxylases suggests that members of this subfamily follow a conserved mechanism for substrate hydroxylation. In contrast, for the alphaKG-dependent non-heme iron halogenase, CytC3, two distinct Fe(IV) complexes form and decay together, suggesting that they are in rapid equilibrium. The existence of two distinct conformers of the Fe site may be the key factor accounting for the divergence of the halogenase reaction from the more usual hydroxylation pathway after C-H bond cleavage. Distinct transformations catalyzed by other mononuclear non-heme enzymes are likely also to involve initial C-H bond cleavage by Fe(IV)-oxo complexes, followed by diverging reactivities of the resulting Fe(III)-hydroxo/substrate radical intermediates.     

The stress response of a semi-infinite micropolar granular material subject to a concentrated force normal to the boundary

We consider the problem of a two dimensional semi-infinite granular material subject to a concentrated or point force normal to the boundary. This boundary value problem was originally solved for a classical elastic material by Flamant in 1892 and, hence, is also known as the Flamant problem (Johnson [8]). In this paper, the granular material is considered as an elastic micropolar or Cosserat continuum and is represented by a particular form of the general constitutive law derived in Walsh and Tordesillas [29]. The stress distribution predicted by the model is in good agreement with experimental data for small strains. In particular, two important features that are captured by the proposed model are: (i) the presence of tensile stress response regions, and (ii) the dependence of the stresses on the microstructural properties, i.e. the particles normal, tangential and rotational stiffness constants. The proposed analysis utilizes two new stress functions, similar to Airys stress functions in classical elastic theory.The support of the US Army Research Office through a grant to AT (Grant No. DAAD19-02-1-0216) and the Melbourne Research and Development Grant scheme is gratefully acknowledged. We thank our reviewers for their useful suggestions and insightful comments.     

Microbeam RBS on flat panel displays

We have demonstrated the utility of microbeam-Rutherford BackScattering (μ-RBS) in spatially resolved studies of operational plasma effects on the interior surfaces of plasma flat panel displays manufactured by Photonics Imaging. The experiments were performed at the Sandia Nuclear microprobe using a 2.8 MeV He beam with an average beam spot size of less than 8 μm. The interior surface of the top panes of the flat panels is composed of approximately 800 nm of MgO on top of a 2000 nm thick PbO layer. μ-RBS of sample panels operated under varying conditions measured changes in the surface MgO film thickness due to plasma erosion and redeposition as accurately as ± 1.5 nm. The high accuracy in the MgO thickness measurement was achieved by inferring the MgO thickness from the shift of the Pb front edge in the RBS spectrum. An estimate for the thickness accuracy as a function of the acquired statistics is presented. The surface of the flat panels' bottom panes is also comprised of MgO on top of PbO. However, troughs 100 μm wide by 10 μm deep were partially filled with phosphor and cover the entire width of the surface. This leaves only 100 μm long sections of MgO within the trough exposed. Using μ-RBS, we were able to analyze the surface composition of these regions.