Publications (45) View all
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Article: Silver nanoparticles deposited on porous silicon as a surface-enhanced Raman scattering (SERS) active substrate.
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ABSTRACT: Silver nanoparticles were deposited spontaneously from their aqueous solution on a porous silicon (PS) layer. The PS acts both as a reducing agent and as the substrate on which the nanoparticles nucleate. At higher silver ion concentrations, layers of nanoparticle aggregates were formed on the PS surface. The morphology of the metallic layers and their SERS activity were influenced by the concentrations of the silver ion solutions used for deposition. Raman measurements of rhodamine 6G (R6G) and crystal violet (CV) adsorbed on these surfaces showed remarkable enhancement of up to about 10 orders of magnitude.Applied Spectroscopy 03/2012; 66(3):294-9. · 1.66 Impact Factor -
Article: Accumulation of explosives in hair--Part 3: Binding site study.
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ABSTRACT: This study extends previous work on the sorption of explosives to the hair matrix. Specifically, we have studied the interaction of 2,4,6-trinitrotoluene (TNT) and triacetone triperoxide (TATP) as a function of chemical pretreatment with acetonitrile, neutral and alkaline hydrogen peroxide, methanolic KOH and potassium permanganate, and the morphological changes that accompany these treatments. While differences in vapor pressure can account for quantitative differences between TNT and TATP sorption, both are markedly affected by the chemical rinses. Examination of the hair surface shows different degrees of smoothening following rinsing, suggesting that the attachment to hair is largely a surface phenomenon involving the 18-methyleicosanoic acid lipid layer. Density functional theory calculations were employed to explore possible nucleation sites of TATP microcrystals on the hair. We conclude that some of the sites on melanin granular surfaces may support nucleation of TATP microcrystals. Moreover, the calculations support the experimental finding that dark hair adsorbs explosives better than light hair.Journal of Forensic Sciences 01/2012; 57(3):623-35. · 1.23 Impact Factor -
Article: Sublimation Rate of Energetic Materials in Air: RDX and PETN
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ABSTRACT: Abstract: This paper reports measurements of RDX and PETN sublimation rate in air. For both explosives the initial samples were prepared by precipitation from solution. For RDX a continuous thin film is obtained, while PETN samples were constituted of small, well separated, single crystals. The sublimation process was monitored using a quartz crystal microbalance (QCM). It is demonstrated that a quantitative description of the sublimation rates can be obtained using molecular diffusion equations in the surrounding air. A quantitative description is limited by the large discrepancy of the reported vapor pressure of these explosives in the literature. An additional obstacle in the accuracy of these predictions is the limited data related to vaporin- air diffusion coefficients. The results reported herein allow us to determine the most relevant vapor pressure source among those reported in the literature and the most probable diffusion coefficient valuesPropellants Explosives Pyrotechnics 01/2012; 37:207-214. · 1.10 Impact Factor -
Article: Molecular dynamics simulations of weak detonations.
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ABSTRACT: Detonation of a three-dimensional reactive nonisotropic molecular crystal is modeled using molecular dynamics simulations. The detonation process is initiated by an impulse, followed by the creation of a stable fast reactive shock wave. The terminal shock velocity is independent of the initiation conditions. Further analysis shows supersonic propagation decoupled from the dynamics of the decomposed material left behind the shock front. The dependence of the shock velocity on crystal nonlinear compressibility resembles solitary behavior. These properties categorize the phenomena as a weak detonation. The dependence of the detonation wave on microscopic potential parameters was investigated. An increase in detonation velocity with the reaction exothermicity reaching a saturation value is observed. In all other respects the model crystal exhibits typical properties of a molecular crystal.Physical Review E 12/2011; 84(6 Pt 1):061122. · 2.26 Impact Factor -
Article: Density-dependent liquid nitromethane decomposition: molecular dynamics simulations based on ReaxFF.
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ABSTRACT: The decomposition mechanism of hot liquid nitromethane at various compressions was studied using reactive force field (ReaxFF) molecular dynamics simulations. A competition between two different initial thermal decomposition schemes is observed, depending on compression. At low densities, unimolecular C-N bond cleavage is the dominant route, producing CH(3) and NO(2) fragments. As density and pressure rise approaching the Chapman-Jouget detonation conditions (∼30% compression, >2500 K) the dominant mechanism switches to the formation of the CH(3)NO fragment via H-transfer and/or N-O bond rupture. The change in the decomposition mechanism of hot liquid NM leads to a different kinetic and energetic behavior, as well as products distribution. The calculated density dependence of the enthalpy change correlates with the change in initial decomposition reaction mechanism. It can be used as a convenient and useful global parameter for the detection of reaction dynamics. Atomic averaged local diffusion coefficients are shown to be sensitive to the reactions dynamics, and can be used to distinguish between time periods where chemical reactions occur and diffusion-dominated, nonreactive time periods.The Journal of Physical Chemistry A 08/2011; 115(36):10181-202. · 2.95 Impact Factor
