Railgun performance with a two-stage light-gas gun injector

Results obtained with the HELEOS (hypervelocity experimental launcher for equation of state) railgun, which uses a two-stage light-gas gun (2SLGG) as an injector, are presented. The high-velocity 2SLGG injector preaccelerates projectiles up to ~7 km/s. The high injection velocity reduces the exposure duration of the railgun barrel to the passing high temperature plasma armature, thereby reducing the ablation and subsequent armature growth. The 2SLGG also provides a column of cool, high-pressure hydrogen gas to insulate the rails behind the projectile, thereby eliminating restrike. A means to form an armature behind the injected projectile has been developed. In preliminary tests, the third-stage railgun has successfully increased the projectile velocity by 1.35 km/s. Extensive diagnostics have been used to determine the behavior of the armature and track the launcher's performance. Insome cases, velocity increases in the railgun section have been achieved, which are in close agreement with theoretical predictions, whereas in other experiments deviations from theoretical have been observed. The reasons for and implications of these results are addressed. Recent tests are reported     

A Review of the U.S. Department of Energy's Inertial Fusion Energy Program

This is the final report of a panel set up by the U.S. Department of Energy (DOE) Fusion Energy Sciences Advisory Committee (FESAC) in response to a charge letter from Dr. Ray Orbach (Appendix A). In that letter, Dr. Orbach asked FESAC for an assessment of the present status of inertial fusion energy (IFE) research carried out in contributing programs. These programs include the heavy ion (HI) beam, the high average power laser (HAPL), and Z-Pinch drivers and associated technologies, including fast ignition (FI). This report, presented to FESAC on March 29, 2004, and subsequently approved by them (Appendix B), presents FESAC's response to that charge.     

Menstruation, menarche, and sexuality in the public school curriculum: school nurses' perceptions

Nurses employed by schools and health departments have varying responsibilities for curricula related to menstruation, menarche, and sexuality. Nevertheless, the school nurse is usually a source of information on these subjects whether employed full-time in school health or also participating in other nursing roles in the community. This survey examines the involvement of school nurses in curricula related to human reproduction including contraception. Data about their involvement in these classroom topics provides a basis for evaluating their roles and making recommendations for subsequent continuing education programs for school health nurses.     

Blends and alloys of vinyl—technology and applications

The use of multiphase polymers is of growing importance because of their inherent economical and technological benefits. The basic characteristics of multiphase polymer blends and alloys are covered. The advantages of vinyl as a component are discussed in light of its ease of processing, inherent compatibility, fire resistance, weatherability, and a wide range of properties achievable. Blend morphology is reviewed and related to the mechanical properties. Typical examples of commercial materials and their application are reviewed.     

A viscoelastic interpretation of miscibility for three PVC-styrenic copolymer blends

The use of multiphase polymers is of growing importance given their inherent economical and technological benefits. Unplasticized PVC is brittle and heat sensitive. Improved impact resistance is often attained by using rubber additives. However, the rubber contributes to increasing viscosity, and, consequently, limited processability. Research efforts are concentrated on the development of a PVC matrix blend that has good heat stability and processability. While traditional PVC modification has concentrated on using plasticizers to aid processing, in this project, the use of three styrenic copolymers has been investigated. Miscibility of the systems has been established using the Rheometrics Mechanical Spectrometer by determining the number of transitions in the resultant blends. Long range time-temperature effects have been established via generation of master curves for the two component systems. The shift factor data has been analyzed to determine the corresponding activation energies associated with different transitions. These indicate a methodology to design optimum blend systems.     

In-situ Vapor-Phase Lubrication of MEMS

In-situ vapor-phase lubrication of sidewall MicroElectroMechanical System (MEMS) devices is investigated with 1-pentanol vapor. The 1-pentanol vapor successfully maintains lubricating properties between silicon contacts of MEMS devices. This is attributed to the ability of alcohol to adsorb on the silicon surface and sustain a lubricating layer, which prevents wear of the MEMS surfaces and minimizes friction. In the presence of these vapors, MEMS devices with sliding contacts operated without failure for up to a factor of 1.7 × 10⁴ longer than in dry N₂ gas alone, representing a dramatic improvement in operating life. Adhesion and friction were also investigated as a function of alcohol vapor pressure. The adhesive force between microfabricated MEMS sidewall surfaces increases from ∼30 to ∼60 nN as the alcohol vapor pressure is increased from 0 to 20% of saturation, and then only slightly increases to ∼75 nN at 95% of saturation vapor pressure. This increase in force is well within the capabilities of even the lowest force on-chip actuators, such as electrostatic comb drives which can typically generate a few μN of force. The static friction force was found to be independent of alcohol vapor pressure within the uncertainties in the measurement.     

High velocity flyer plate launch capability on the Sandia Z accelerator

A method has been developed for launching plates useful for equation of state (EOS) studies to high velocities using fast pulsed power on the Sandia National Laboratories Z Accelerator. The technique employs magnetic pressure developed in an insulating gap between the anode and cathode of the machine to provide smoothly increasing, quasi-isentropic loading to plates of 9 – 12 mm in diameter and hundreds of microns thickness. Successful launches of titanium to 12km/s, aluminum to 13km/s, and copper to 10km/s have been demonstrated. The plates were monitored through the entire launch process with both conventional and spatially resolved velocity interferometry to obtain acceleration histories and impact profiles. Impacts of the flyers into aluminum wedges were also performed to experimentally estimate final plate thickness. Initial indications are that the plates are intact, slightly bowed, and at essentially ambient state.     

Experimental determination of ultrasonic wave velocities in plastics as functions of temperature. IV. Shear velocities in common plastics

The temperature dependence of acoustic shear velocities are reported for Poly-Penco nylon, type G Plexiglass [poly(methyl methacrylate)], TFE Teflon (tetrafluoroethylene), low- and high-density polyethylene, Lexan (polycarbonate), and Delrin Acetal (nylon). Most of the data were obtained at a frequency of 1 Mc./sec. over the temperature range of 25–100°C. In addition, previously unreported longitudinal velocities to ～125°C. are reported for Lexan and Delrin Acetal.     

Hypervelocity Jet Initiation Threshold Criteria of Nitromethane and Nitromethane Mixtures

The experimental hypervelocity jet initiation threshold criteria for neat nitromethane and homogeneous- and heterogeneous-sensitized nitromethane mixtures have been determined over a range of failure diameters, jet velocities from 2–9 mm/μs, and jet diameters in two test configurations. These criteria were used to define detonation and failure conditions in nitromethane and the nitromethane mixtures as a function of contact- and bow-shock conditions. These data were compared with data reported by others in the literature on bare solid explosives. A favorable comparison of threshold values is achieved by normalization of the criteria with the failure diameters. The effect on the initiation of the confinement proximity to the jet axis was also investigated. Experimental results have shown that high impedance boundaries near the jet axis induced conditions that allowed initiation to occur at lower jet velocities than those determined by the criteria. Tests also were performed on both homogeneous and heterogeneous nitromethane mixtures, having the same failure diameters, to determine if the same or similar jet penetration distances were required for initiation. The results, within experimental error, do not show any definitive differences in initiation conditions between the two types of mixtures.     

Ignition Characteristics of Metastable Intermolecular Composites

Metastable Intermolecular Composite (MIC) materials are comprised of a mixture of oxidizer and fuel with particle sizes in the nanometer range. They are a subclass of materials known as thermites. The mechanism responsible for the propagation of reaction in loose compacts is not well understood. We have conducted a series of experiments using high‐speed photography and pressure transducers in an attempt to identify the dominant mechanism. We studied a mixture of aluminum and molybdenum trioxide. Of the four possible candidates (radiation, convection, conduction, and acoustic/compaction), these preliminary studies identify convection as the most likely. However, the extent of contribution of the other modes is not yet known and this will receive further study.