Uncoated Targets Research Articles

Study on the penetration resistance of a honeycomb composite structure coated with polyurethane elastomer

In this study, the ballistic performance of the composite structure was investigated and studied by experiment and finite element analysis in order to study the anti-penetration performance of a polyurethane elastomer-coated honeycomb sandwich construction. Six kinds of target plate structures with different configurations were prepared by changing the hard segment content and coating position of polyurethane elastomer. The first-stage light gas gun device is used to conduct impact experiments at various speeds, and the finite element simulation computation is performed using LS-DYNA. Based on the experimental and finite element results, the ballistic limit velocity and specific energy absorption of different target configurations were analyzed, and the failure forms, damage areas, and failure mechanisms were discussed. The findings demonstrate that the polyurethane elastomer coating enhances the honeycomb sandwich structure’s ballistic limit performance by 40.6% to 51% and that the honeycomb core of the target plate with the coating on the front panel has a larger area of collapse. This fully exploits the benefits of the honeycomb structure in the energy absorption process and makes up for the weaknesses of the honeycomb sandwich structure’s subpar energy absorption effect under local impact loads. Therefore, the front panel coating has better ballistic limit performance. The coated polyurethane with medium hardness demonstrated the best ballistic limit performance for the various polyurethane hardness. The ballistic limit speeds of the front panel and back panel coatings increased by 51% and 48.8% respectively, in comparison to the uncoated target plate. After comparing the structure of polyurea coating, it is found that the ballistic limit performance of polyurethane coating with medium hardness is higher than that of polyurea coating structure, and the negative growth of the ballistic limit performance of the whole structure caused by the coating of rigid polyurea on the back panel is effectively avoided.

Measurements of laser-imprint-induced shock velocity nonuniformities in plastic targets with the Nike KrF laser

We report results of direct-drive laser imprint experiments measuring velocity perturbation profiles of shock waves produced by the Nike krypton fluoride laser. A new high-resolution two-dimensional velocimeter system was successfully implemented on the Nike laser facility and used for sensitive optical measurements of the velocity perturbations. Planar polystyrene targets with and without a thin high-Z overcoat (400 Å Au or 600 Å Pd) were irradiated by four, eight, and sixteen Nike laser beams to examine laser imprint and its mitigation. The results from the uncoated targets showed that the shock velocity perturbations decreased with an increasing number of laser beams overlapped on target, precisely as anticipated by the beam averaging effect on laser imprint. In the experiment on the shocks driven in the high-Z coated targets, the shock velocity perturbations were further reduced by a factor of 2–6 compared to their counterparts in the uncoated experiment, with the amplitude of the velocity fluctuations measured as small as 20 m/s rms for shock velocities of 20 km/s. These experiments allowed more direct measurements of laser imprint effects without relying on the Rayleigh–Taylor hydrodynamic amplification, providing valuable quantitative data for calibrating radiation-hydrodynamic simulations of laser imprint.

Enhancement of Kα emission through efficient hot electron generation in carbon nanotubes on intense laser pulse irradiation

Near complete absorption of the energy of intense ultra-short laser pulses (45 fs, intensity ∼1.6 × 1016 to 2.5 × 1017 W/cm2) is observed in carbon nanotubes deposited on a planar molybdenum substrate. The hollow structure of the nanotube plasma facilitates resonant electric field enhancement during its ionization phase. This resonantly enhanced localized field at a density much larger than the critical density nc leads to efficient hot electron generation, which results in enhanced Kα emission of Mo at 17.5 keV. It is observed that for nanotubes, depending on the degree of hollowness, there is an optimum laser intensity for maximum x-ray enhancement compared to a planar uncoated target.

Laser-accelerated ions from layered targets

We investigated laser-driven ion acceleration with tightly focused femtosecond laser pulses at an intensity of 5×10 19 W/cm 2. Targets consisting of thin metal foils either back-coated with a μ m -thick dielectric layer or uncoated have been used. The observations we report show that proton bunches with energy in the MeV range have been produced. Furthermore, the protons emitted from back-coated targets exhibit a spatial cross-section which is remarkably more uniform and of significantly smaller size if compared with that of the protons emitted from uncoated foils. The experimental results are discussed in terms of the differences between the propagation of the fast electron current inside the back-coated and uncoated targets.

Enhanced generation of fast protons from a polymer-coated metal foil by a femtosecond intense laser field

The results of generation of fast protons from 5-μm-thick copper foil targets by 60fs laser irradiation at 1.5×1017W∕cm2 are presented. Both polyvinylmethylether (PVME)-coated and uncoated copper foil targets are examined. Fast protons are measured using a Thomson mass spectrometer and maximum proton energies are 570 and 280keV for the PVME-coated and the uncoated target, respectively. The intensity of fast protons with energy of 160keV from the PVME-coated target is approximately 80-fold higher than that from the uncoated target.

Laser driven shock wave studies in gold coated Plexiglas targets

Abstract Laser-driven shock wave propagation in a transparent material such as Plexiglas coated with a thin overlayer of gold is studied using the technique of high speed optical shadowgraphy. A Nd: glass laser was focussed to produce intensities in the range of 10′2-10′4W/cm2 on the target, within an irradiation spot diameter of 160 pm, optical shadowgrams were recorded bya second harmonic (0.53 pm wavelength) pulse. Shock pressures and scaling of pressure with laser intensity was studied. Shock pressures in gold-coated Plexiglas target was observed to be considerably higher compared to those in uncoated targets. This enhancement of shock pressure has been explained on the basis of contribution of an X-ray driven ablative heat wave in the gold plasma. Shock pressure values show a close agreement with those obtained from a one-dimensional Langrangian hydrodynamic simulation. Shadowgrams of shock fronts produced by non-uniform spatial laser beam irradiation profiles have shown complete smoothing when a gol...

Study of laser-driven shock wave propagation in Plexiglas targets

An experimental study of laser-driven shock wave propagation in a transparent material such as Plexiglas using a high-speed optical shadowgraphy technique is presented in this paper. A Nd:glass laser was used to produce laser intensity in the range 1012-1014 W/cm2 on the target. Optical shadowgrams of the propagating shock front were recorded with a second-harmonic (0.53-μm) optical probe beam. Shock pressures were measured at various laser intensities, and the scaling was found to agree with the theoretically predicted value. Shock pressure values have also been obtained from a one-dimensional Lagrangian hydrodynamic simulation, and they match well with experimental results. Shadowgrams of shock fronts produced by nonuniform spatial laser beam irradiation profiles have shown complete smoothing when targets with a thin coating of a material of high atomic number such as gold were used. Shock pressures in such coated targets are also found to be considerably higher compared with those in uncoated targets.

Quantitation of conjugate formation between human polymorphonuclear leukocytes and antibody-coated target cells by flow cytometry: the role of Fc receptor and LFA-1 antigen.

The specific binding of human polymorphonuclear leukocytes (PMN) to antibody-coated target cells was characterized by flow cytometry. PMN were labeled with phycoerythrin-E (PE) via a granulocyte-specific monoclonal antibody (leu-M1) and mixed with fluorescein isothiocyanate-labeled K562 tumor cells sensitized with rabbit antiserum. Specific conjugates were formed as analyzed by two-color fluorescence in a flow cytometer. The formation of stable conjugates was dependent on initiation of contact, temperature, time, and antiserum concentration. Studies with inhibitors implicate that microfilaments, but not microtubules, Ca2+, Mg2+, or energy-dependent processes were a prerequisite for binding of PMN to the antibody-coated target cells. No conjugates were formed when uncoated target cells were used or when the experiment was performed in the presence of protein A, indicating that binding was specifically mediated through Fc receptors (FcR). Monoclonal antibodies against the FcRII and FcRIII were used to address the role of these receptors in conjugation. One of the two anti-FcRIII antibodies and an anti-FcRII antibody effectively prevented conjugation. A monoclonal antibody directed against the common beta-chain of the adhesion molecule family and a combination of antibodies against the alpha-chain of LFA-1 and Mo-1 also blocked conjugation when target cells were sensitized under suboptimal conditions. The antibody against the beta-chain also diminished killing of antibody-coated K562, as measured by chromium release when included in the cytotoxicity assay. These results indicate that flow cytometry permits accurate quantitation and characterization of the binding between PMN and antibody-coated target cells, which in principle, can be prevented by monoclonal antibodies against surface receptors. Binding is primarily established by both the FcRII and FcRIII. Adhesion-associated molecules on the PMN surface contribute to optimal binding.

Antibody-dependent cytolysis (ADCC) of tumor cells by activated murine macrophages is a two-step process: Quantification of target binding and subsequent target lysis

To analyze the antibody-dependent cell-mediated cytotoxicity (ADCC) reaction between tumor cells and activated murine macrophages in detail, it must be first determined if physical binding occurred between the two cell types. Over 15–20 min in vitro, antibody-coated HSB neoplastic targets became so firmly attached to the activated macrophages that they resisted removal with 4 vigorous washes. When a quantitative assay of binding was employed, attachment of tumor cells to activated macrophages was found to depend on the concentration of antibody and on the density of the macrophages. These two variables also determined the subsequent extent of cytolysis. Binding of antibody-coated targets by macrophages elicited with thioglycollate broth or activated by bacillus Calmette-Guerin (BCG) was comparable. Lysis by the activated macrophages, however, was far greater. Binding occurred at 4, 22, or 37 °C, while the subsequent lytic reaction occurred only at 37 °C. Thioglycollate broth effectively inhibited lysis but had no effect on binding. A porous filter placed between activated macrophages and targets resulted in abrogation of binding and lysis, even when antibody-coated targets were placed beneath the filters. When labeled, uncoated targets were added to cultures of macrophages in the presence of unlabeled antibody-coated targets, no lysis of the bystander (i.e., uncoated) targets was seen. The data suggest that ADCC is a multistep reaction, that vigorous physical binding of antibody-coated targets by activated macrophages is an initial and necessary step in ADCC, that such binding is not sufficient for ADCC, that such binding controls the selectivity of lysis in ADCC, and that the second step in ADCC results in target lysis.

Antibody-Dependent Cell-Mediated Cytotoxicity

Lymphoid cells from nonsensitized donors can be cytotoxic in vitro for target cells coated with antibody. The antibody can be directed either against antigens which are intrinsic to or experimentally attached to the target cell surface. Killing of target cells by this method has been termed antibody-dependent cell-mediated cytotoxicity (ADCC). In these investigations we compared the ability of Peyer's patch cells and spleen cells from nonsensitized mice to lyse lipoplysaccharide-coated and uncoated target cells by an ADCC mechanism. The results demonstrate that spleen cells, but not Peyer's patch cells, from identical mice can be cytotoxic for lipopolysaccharide-coated chicken erythrocytes (CRBC) in the presence of anti-lipopolysaccharide antibody and uncoated CRBC in the presence of anti-CRBC antibody. Thus, Peyer's patches in mice appear to be deficient in the effector cell type(s) required to kill antibody-coated erythrocyte target cells by an ADCC mechanism as well as the macrophage-like accessory adherent cell type(s) required for the induction of humoral antibody synthesis and cell-mediated cytotoxic allograft reactions in vitro.

Laser-induced stresses in coated and uncoated targets

A number of experiments were conducted with a pulsed Nd:glass laser to assess the effect of thin coatings with varying optical properties on laser coupling and stress wave generation in aluminium targets. The coatings included liquid cement, which is transparent at 1.06 mu m; Aquadag which is opaque; and silver paint, which ranges from translucent to opaque, depending upon the curing time. Considerable stress enhancement was found for the transparent plasma-confining coatings and the partially cured silver paint, which was semitransparent and contained a volatile binder. Stress levels for untreated aluminium and samples with Aquadag or cured silver paint coatings varied approximately with the coupling coefficient for these materials. The potential ramifications of these results to laser-fusion experiments are discussed.