Effect of surface plasmon excitations on the irradiance pattern of the return beam in optical disk data storage

The excitation of surface plasmons at a dielectric-metal interface is responsible for dips in the zeroth order diffraction efficiency of a metal grating at certain angles of incidence. The dips appear as dark bands in the returning irradiance pattern in an optical disk system and are seen only when there is a component of incident polarization that lies perpendicular to the tracks. The location of these bands is derived from theoretical considerations and is shown to depend on the track pitch and the materials involved, but not on the groove depth or width. The band locations are confirmed by zeroth order diffraction efficiency measurements as a function of incident angle. A possible negative effect of these bands on an optical disk system is the introduction of additional fluctuations and noise into the focusing and push-pull tracking signals.     

Interaction of lactoferrin, monocytes, and T lymphocyte subsets in the regulation of steady-state granulopoiesis in vitro

Colony-stimulating activities (CSA) are potent granulopoietic stimulators in vitro. Using clonogenic assay techniques, we analyzed the degree to which mononuclear phagocytes and T lymphocytes cooperate in the positive (production/release of CSA) and feedback (inhibition of CSA production/release) regulation of granulopoiesis. We measured the effect of lactoferrin (a putative feedback regulator of CSA production) on CSA provision in three separate assay systems wherein granulocyte colony growth of marrow cells from 22 normal volunteers was stimulated by (a) endogenous CSA-producing cells in the marrow cells suspension, (b) autologous peripheral blood leukocytes in feeder layers, and (c) medium conditioned by peripheral blood leukocytes. The CSA-producing cell populations in each assay were varied by using cell separation techniques and exposure of isolated T lymphocytes to methylprednisolone or to monoclonal antibodies to surface antigens and complement. We noted that net CSA production increased more than twofold when a small number of unstimulated T lymphocytes were added to monocyte cultures. Lactoferrin's inhibitory effect was also T lymphocyte dependent. The T lymphocytes that interact with monocytes and lactoferrin to inhibit CSA production are similar to those that augment CSA production because their activities are neither genetically restricted not glucocorticoid sensitive, and both populations express HLA-DR (Ia-like) and T3 antigens but not T4 or T8 antigens. These findings are consistent with results of our studies on the mechanism of lactoferrin's inhibitory effect with indicate that mononuclear phagocytes produce both CSA and soluble factors that stimulate T lymphocytes to produce CSA, and that lactoferrin does not suppress monocyte CSA production, but does completely suppress production or release by monocytes of those factors that stimulate T lymphocytes to produce CSA. We conclude that mononuclear phagocytes and a subset of T lymphocytes exhibit important complex interactions in the regulation of granulopoiesis.     

Fast Burning Rocket Propellants Based on Silicone Binders – New Aspects of an Old System

Fast burning rocket propellants based on ammonium perchlorate (AP) and polydimethylsiloxane (PDMS) binders have been formulated and basically characterized in aluminized and non aluminized versions. The thermodynamic performance of PDMS bound propellants is limited by the evaporation point of silicon dioxide (crystobalite at 2863 K), which is formed during the combustion. The maximum specific impulses calculated with an expansion ratio of 70 : 1 are I_SP = 2340 N s/kg (238 s) for AP/PDMS and I_SP = 2430 N s/kg (247 s) for AP/Al/PDMS formulations. With a tri‐modal AP‐fraction of 200 μm, 30 μm and 2 μm it was possible to achieve processable propellants with 83% and 84% solid loading. They give burning rates close to 60 mm/s at 10 MPa and pressure exponents between 0.5 and 0.6 in the range of 7–25 MPa. The thermodynamic specific impulse of these systems was calculated to I_SP=2319 N s/kg (236 s) for AP/PDMS and I_SP=2403 N s/kg (245 s) for AP/Al/PDMS formulations at 70 : 1 expansion ratio. Measurements of the glass transition point by DMA and TMA detected a time dependent partial crystallization of the used PDMS close to T_G in the temperature range from −44 °C to −60 °C. Basic tests reveal high thermal and chemical stability with flash points over 300 °C and zero detonation sensitivity at 50 mm diameter. The property profile, so far determined, tends to fulfil the demands for applications as propellants with high burning rates and operating pressures together with a high thermal stability and a low vulnerability.     

Characteristic Properties of an End Burning Grain with Smoke Reduced Ferrocene Containing Composite Propellant

Design, formulation and properties of an end burning grain are described which works for underwater propulsion operating at the level of 1200 N thrust for 20 s burning time. To avoid cavitational noise the formation of hot particles must be prevented. For this reason a smoke reduced composite propellant based on AP/HTPB with 86% energetic solids including 14% HMX and with 1% ferrocene derivative was adapted to grain size and motor configuration. For inhibition a pyrolytically stabilized polyurethane insulation was applied. The thermal insulation was made from a stiff high temperature resistant phenolic resin. The propellant exhibited a smooth burning behaviour with good processibility and mechanical properties. The desired performance was delivered at 120 bar operating pressure connected to 165 mm grain diameter and 93% thrust efficiency. Looking closer to the system it was found that part of the ferrocene derivative and plasticizer migrated from the propellant block to the inhibition layer. In the course of migration a small change of burning but a larger change of mechanical properties occurred in the boundary of the propellant. Despite these disadvantages burning times of 5 s and 10 s had been successfully realized with a case bonded configuration. For larger grain sizes, however, cracks occurred around the surface of the cylindrical propellant block. Calculation of the mechanical stresses which built up upon thermal shrinkage after curing and cooling showed values higher than the mechanical strength of the propellant could fit. These problems finally were overcome by a free standing grain. It led to a successful function of the motor for burning times of 20 s and more.     

Detection of Radicals at the Photolysis of tert-Butyl Hydroperoxide in DMSO and water

The decomposition of tert-butyl hydroperoxide by photochemically induced reactions in DMSO

1 Abbreviations used: DMSO, dimethyl sulfoxide; DMSO-d₆, completely deuterium labelled dimethyl sulfoxide; cw-ESR, continuous-wave Electron Spin Resonance; u. v., ultra violet; DMPO, 5, 5-dimethyl-I-pyrroline N-oxide; TMPO, 3, 3, 5, 5-tetramethyl-l-pyrroline N-oxide.

and water was investigated by cw-e.s.r. spectroscopy. The products tert-butylperoxyl, methyl and sulfur-centered free radicals were identified. The tert-butoxyl free radical is involved in the primary process as shown by time-resolved e.s.r. technique. On the basis of directly identified radical species, a mechanism for the photochemically induced reactions of tert-butyl hydroperoxide in DMSO is proposed. At concentrations below 0.8 mol · l⁻¹ the radical formation from tert-butyl hydroperoxide proceeds by cleavage of the O O bond rather than by hydrogen abstraction.