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  • 1995-1999  (9)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1749-1753 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An investigation has been carried out into the differences between the deflagration-to-detonation (DDT) process as it occurs in low density [∼30% theoretical maximum density (TMD)] columns of conventional grain size (∼180 μm) pentaerythritol tetranitrate (PETN) and in ultrafine PETN with a grain size ∼1 μm. The principle technique for observing the process utilized charges confined within a steel housing fitted with a polycarbonate slit window. This allowed direct recording of the transition using high speed streak photography. The explosive was thermally ignited using a pyrotechnic mixture with low gaseous emission to minimize any prepressurization of the charge. In addition to the photographic records of the events, the outputs of photodiodes along the length of the column were monitored in order to determine the rate at which the reaction proceeds. The results obtained show that the DDT process in the larger grain PETN at low density was similar in structure to the DDT process at higher densities. In contrast a different mechanism leads to detonation in columns composed of the smaller grain size PETN when packed to densities less than 50% TMD. After ignition hot gases propagate along the column both compacting and igniting material as they pass. After the gases have reached the downstream end of the column, the column continues to burn and the pressure and temperature increase. Some time later initiation takes place at a point along the burning column, and detonation waves propagate in both directions from this point. The detonation waves propagate from the initiation point at speeds that would normally be associated with material compacted to around 60% TMD. The process appears to be in effect a deflagration-to-localized thermal explosion detonation transition. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3736-3739 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A mechanism for the compressive failure of soda-lime and borosilicate glasses is proposed based upon high-speed photography of impact on glasses. Shock loading was produced by the impact of a 50 mm diameter projectile so inducing shock states of one-dimensional strain in glass targets. The shock waves and failure fronts were visualised using the shadowgraph technique. The failure appeared to occur at discrete nucleation sites and propagated out to form a continuous front. The velocity of this front increased with higher impact stresses and varied with the glass composition. © 1995 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6707-6709 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lateral stress measurements in a tungsten alloy, in combination with known Hugoniot data, have been used to find the shear strength of this material, and its variation with longitudinal shock stress, up to 14 GPa. Results show that the shear strength increases significantly with increasing stress. Prior to this work, there has been disagreement in the literature on the effect of shock stress on the shear strength of tungsten and its alloys. The present work agrees with the data obtained by Zhou and Clifton [J. Appl. Mech. 64, 487 (1997)] who used pressure shear. However, the range of stresses studied has been greatly extended. © 1999 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Public Health 19 (1998), S. 335-358 
    ISSN: 0163-7525
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine
    Notes: Abstract Cigarette smoking continues to place an enormous burden on US health systems. The treatment of tobacco-dependent persons is vital to the public health, since unmitigated smoking could lead to the development of disease and premature death in as many as 20 million current smokers in the United States. Much of this tobacco-related morbidity and mortality could be prevented by the application of existing treatments, as well as newer ones. Access to safe and effective treatments was significantly expanded in 1996, when two forms of nicotine replacement therapy (NRT), the nicotine gum and patch, became available for over-the-counter sale. Expanded access has led to significantly increased utilization and quitting. Even with these advances, however, the scope of this tobacco dependence demands that we explore alternative treatment strategies, including exposure reduction therapy (ERT) as a possible option for smokers not currently making quit attempts. In this review, we present principles to guide the development of such a therapy, and for its application, should it be proven effective.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 734-738 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The response to plate impact loading of three aluminas with varying glass content and porosity has been investigated. Spall strengths have been shown to be dependent on the amplitude and duration of the compression pulse which precedes the tensile loading, but insensitive to the rate of release. Some tensile strength is measured in impacts where the Hugoniot elastic limit has been exceeded. The effect of the material microstructure on the dynamic tensile strength has also been studied. Low porosity aluminas with many microstructural irregularities were found to possess the lowest spall strengths. Experimental values compare well with those predicted by an energy balance theory developed by Grady [J. Mech. Phys. Solids 36, 353 (1988)]. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3842-3847 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of laser radiation from a Nd/glass laser with single crystals of cyclotrimethylene trinitramine (RDX) secondary explosive and RDX slices (cleaved from larger crystals of RDX) has been studied by high-speed framing photography with microsecond interframe times. Decomposition and deflagration were recorded following ignition at localized regions or "hot spots.'' © 1996 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3499-3503 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The deflagration-to-detonation transition process has been observed in pressed granular columns of the explosive pentaerythritol tetranitrate. Charges were confined within a steel housing which had been fitted with a polycarbonate window to allow direct recording by high-speed streak photography. The explosive was thermally ignited by a gasless pyrotechnic mixture to minimize pre-pressurization of the charge. The results indicate that upon ignition, early choked flow of the combustion gases prevents the continued propagation of the combustion via a convective heat transfer mechanism and that the propagation of reaction becomes governed by a leading compaction wave which causes ignition through the mechanical formation of hot spots. Detonation finally occurs when the leading front of an accelerating plug of highly compacted material (density close to the theoretical maximum) formed between the reaction front and the leading compaction wave, attains the critical pressure necessary for shock-to-detonation transition. © 1996 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4423-4427 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cylindrical cavities, viewed through the side as they collapsed onto solid surfaces, were studied using high-speed streak and framing photography. The cavities were collapsed asymmetrically using shock waves of varying amplitude so that the rear surface formed a high-speed jet which crossed the cavity and interacted with the target surface. Schlieren optics were used to visualise waves in the fluid and in the target. Two features of the collapsing bubble affected the damage to the target surface. The first was the impact of the high-speed liquid jet on either the rear wall of the cavity or the target itself. The second was the production of a strong compression wave on the rebound of the bubble after it reached minimum volume. Damage to the targets related to their material properties. Metals, with low compressive but higher tensile strengths, plastically deformed beneath the penetrating jet to form a pit. Brittle materials, with high compressive but low tensile strengths, deformed by cracking. The position of the cavity relative to the surface had a major effect upon the geometry of the damage. With the cavity close to the target, the penetrating jet dominated the damage leaving single pits. With the cavity at some distance, the rebound wave was more important than the jet giving rise to a circular damage mark. This mechanism can be used to re-interpret previous experimental observations [Y. Tomita and A. Shima, J. Fluid Mech. 119, 535 (1986)]. © 1995 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1643-1649 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study is described of the impact process and the corresponding surface damage to PMMA (polymethylmethacrylate) targets impacted by ice and nylon spheres. A gas gun system was used to project the spheres and the impacts were recorded using a high-speed image converter camera (Imacon 792). Special attention was paid to the conditions causing projectile failure and the surface damage to the target. The experimental results show that although the deformation and failure modes for ice and nylon are different, the surface damage to the PMMA target has a similar failure pattern, i.e., a central, circular undamaged region surrounded by an annular damaged region containing many short circumferential cracks. Analysis shows that the diameter d of the central undamaged region and the annular damaged area Am can be used to characterize the surface damage which depends on the projectile material, sphere radius R, as well as the impact velocity V0. For a given projectile, two critical impact velocities exist: One is the threshold velocity (V0)th, below which no visible surface damage is observed, and another is the fracture velocity (V0)f, above which a plate target is broken. Damage in the annular region is caused by the Rayleigh surface wave in the present experiments. The conditions for the Rayleigh surface wave to pass ahead of the expanding edge contact velocity are analyzed. Comparisons between the theoretical predictions and experimental results, including the present study and earlier data, are made for PMMA plates impacted by projectiles of different materials (ice, nylon spheres, and water drops) and at different impact angles. © 1995 American Institute of Physics.
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