Structure-property relationship of HTPB-based propellants. I. Effect of hydroxyl value of HTPB resin

Composite propellants based on hydroxyl-terminated polybutadience (HTPB) resin are the most common contemporary solid propellants for launch vehicle and missile applications. A series of HTPB resins, manufactured by free-radical polymerisation using a peroxide initiator, with varying molecular weights and hydroxyl values, was used in propellant formulation experiments with a view to studying the resin production variables and their influence on the resultant propellant properties. It is seen that HTPB resins with a wide range of hydroxyl values could be effectively utilized in propellant formulations. Also, propellants with higher strain capability and chain flexibility could be produced from lower hydroxyl value resins. © 1993 John Wiley & Sons, Inc.     

Electroplating of Nickel Using a Modified Barrel Design

Nickel is a metal electroplated on a wide variety of articles both ferrous and nonferrous. Small articles which are difficult to jig are frequently plated by barrel plating technique.

In conventional barrel plating the parts to be plated are contacted by either a rod, dangler or metallic wall as they rotate inside the barrel. A modified barrel design has been effected by changing the dangler contact with uniformly distributed contact tips at varying points on the periphery of the barrel. A modification in anode positioning is also made. Improvement in thickness uniformity brought about by use of this modified design are reported in this paper.     

Recent advances in mammalian radiation genetics and their relevance to the problem of genetic risk estimates in man

Current estimates of the genetic hazards arising from the exposure of human populations to radiation are to a large extent, based on the results obtained with experimental organisms, especially laboratory mammals. During the past few years there has been substantial progress in the field of mammalian radiation genetics; some of the findings have confirmed and extended earlier ones while others have exposed new and interesting facets of the radiation response of the mammals. The present review is devoted to an examination of some of the recent results from the standpoint of their applicability to the problem of genetic risk estimates in man.     

Validating numerical semidefinite programming solvers for polynomial invariants

Semidefinite programming (SDP) solvers are increasingly used as primitives in many program verification tasks to synthesize and verify polynomial invariants for a variety of systems including programs, hybrid systems and stochastic models. On one hand, they provide a tractable alternative to reasoning about semi-algebraic constraints. However, the results are often unreliable due to “numerical issues” that include a large number of reasons such as floating-point errors, ill-conditioned problems, failure of strict feasibility, and more generally, the specifics of the algorithms used to solve SDPs. These issues influence whether the final numerical results are trustworthy or not. In this paper, we briefly survey the emerging use of SDP solvers in the static analysis community. We report on the perils of using SDP solvers for common invariant synthesis tasks, characterizing the common failures that can lead to unreliable answers. Next, we demonstrate existing tools for guaranteed semidefinite programming that often prove inadequate to our needs. Finally, we present a solution for verified semidefinite programming that can be used to check the reliability of the solution output by the solver and a padding procedure that can check the presence of a feasible nearby solution to the one output by the solver. We report on some successful preliminary experiments involving our padding procedure.     

Extraordinary Macroscale Wear Resistance of One Atom Thick Graphene Layer

During the last few years, graphene's unusual friction and wear properties have been demonstrated at nano to micro scales but its industrial tribological potential has not been fully realized. The macroscopic wear resistance of one atom thick graphene coating is reported by subjecting it to pin‐on‐disc type wear testing against most commonly used steel against steel tribo‐pair. It is shown that when tested in hydrogen, a single layer of graphene on steel can last for 6400 sliding cycles, while few‐layer graphene (3–4 layers) lasts for 47 000 cycles. Furthermore, these graphene layers are shown to completely cease wear despite the severe sliding conditions including high contact pressures (≈0.5 GPa) observed typically in macroscale wear tests. The computational simulations show that the extraordinary wear performance originates from hydrogen passivation of the dangling bonds in a ruptured graphene, leading to significant stability and longer lifetime of the graphene protection layer. Also, the electronic properties of these graphene sheets are theoretically evaluated and the improved wear resistance is demonstrated to preserve the electronic properties of graphene and to have significant potential for flexible electronics. The findings demonstrate that tuning the atomistic scale chemical interactions holds the promise of realizing extraordinary tribological properties of monolayer graphene coatings.     

AB‐type crosslinked polymer networks from vinyl terminated polyurethane and poly(methyl methacrylate)

Vinyl terminated polyurethanes (VTPUs) were prepared by endcapping isocyanate terminated prepolymers with vinylbenzyl alcohol (VBA). AB‐type crosslinked polymer (ABCP) networks were generated by crosslinking the telechelic polyurethane with methyl methacrylate (MMA) in the presence of 2,2′‐azobisisobutyronitrile (AIBN) as free radical initiator. The spectral, thermal and mechanical properties of ABCPs were studied using Fourier Transform IR, thermogravimetry, dynamic mechanical analysis and stress‐strain analysis. The FTIR results confirm the formation of VBA, TP and ABCPs. Thermal behaviour of crosslinked polymers showed no significant weight loss up to 300 °C, indicating improved thermal stability. Dynamic mechanical tests revealed confinement of phase separation and good damping behaviour for the crosslinked networks. Stress‐strain analysis showed that tensile strength increases with increasing amounts of methyl methacrylate. © 2001 Society of Chemical Industry