Interior ballistics of a hybrid electromagnetic gun

The dynamics for the projectile inside an electromagnetic gun has been developed. The gun consists of a series of stationary cylindrical coils that are pulsed and of one inner concentric coil driven at constant current. The inner coil is the projectile. Two important design parameters are identified: one is the desired exit velocity divided by the square root of the number of stationary coils, the other is a characteristic time related to the rapidity with which the projectile attains its maximum velocity in any stationary coil.     

Measuremeints on Current Sheets in Plasmas

The acceleration of a gas undergoing ionization in a crossed electric-magnetic field leads to the formation of current sheets similar to those observed in coaxial plasma guns. The dynamics of such sheets is of great interest to workers in plasma physics in view of their application to controlled thermonuclear fusion experiments and to space propulsion. In the present paper a detailed mapping of the magnetic field in the vicinity of a current sheet is described. Conventional small search coils are used for the detection of this field. From the configuration of this field an attempt is made to understand the processes taking place in the sheet. All of the experiments described in the paper are performed on a plasma coaxial gun of mall aspect ratio.     

Numerical Simulations of an Optical Fiber Drawing Process Under Uncertainty

Manufacture of optical fibers is subject to inherent uncertainty in various process and material parameters, which, in turn, leads to variability in product quality and impacts the reliability of the optical fibers in use. Analysis of the interactive effects of parameter uncertainty on the optical fiber quality is imperative in a robust-design endeavor. To this end, a methodology for simulation of optical fiber drawing process under uncertainty is presented by considering a two-dimensional (2D) numerical model of the flow, heat and mass transfer phenomena involved in the fiber drawing process. A sampling-based stochastic model is developed, and parametric analysis is presented to elucidate the effects of uncertainty in several process and material parameters on the variability of index of refraction, residual stress, maximum tension, and defect concentration. Design maps are derived from the analysis which provide for selection of furnace wall temperature as a function of the input parameter uncertainty and target maximum acceptable variability in the index of refraction, residual stress, maximum tension, and defects.     

Simulation of sintering of nanoparticulate micropreforms in a microfabrication process

Microcasting is a technique for fabricating ceramic and metallic microstructures and involves sintering of a nanoparticulate green body as the final step to produce the microparts. The sintering kinetics at the nanoparticulate scale determines the local sintering stress throughout the micropreform, which, in turn, affects the overall shape deformation of the final sintered products. This paper presents a numerical analysis on the coupled sintering processes using a viscous sintering mechanism to illustrate the methodology for multiscale simulations. A microscopic model for viscous sintering is adopted to describe the micro/nanostructural evolution by considering the effects of nanoparticle mechanics on the sintering kinetics. The overall dimensional change of the sintered micropart is determined based on the local sintering stress in the green body, which is evaluated using the evolution of the micro/nanostructure during sintering. The multiscale model is used to explore the effects of the various material and process parameters on the shape evolutions during sintering and on the final sintered shape of microparts.     

Fast superconducting storage systems

A review of the requirements for a fast superconducting inductive pulsed storage system is presented. The discussion includes in particular, the important characteristics of the components of the pulsed source: the high current source, the switch and the energy transfer scheme. In addition, a proposed superconducting pulsed source incorporating some of these characteristics is described.     

Design of microresonators under uncertainty

A methodology for robust design analysis of microelectromechanical systems is presented by considering the example of comb microresonators and uncertainty in parameters governing the resonant frequency and the transconductance values. Analytical models for the variability in the resonant frequency and transconductance are developed as function of the parameter uncertainty, and used as objective functions sought to be minimized in a robust design endeavor. An enumeration search over the design space is utilized to determine the optimal design of microresonators that minimize the variability subject to constraints on performance requirements. The results are presented over a wide interval of operating resonant frequency, and can be used in the robust design of microresonators.     

Locally Secreted Semaphorin 4D Is Engaged in Both Pathogenic Bone Resorption and Retarded Bone Regeneration in a Ligature-Induced Mouse Model of Periodontitis

It is well known that Semaphorin 4D (Sema4D) inhibits IGF-1-mediated osteogenesis by binding with PlexinB1 expressed on osteoblasts. However, its elevated level in the gingival crevice fluid of periodontitis patients and the broader scope of its activities in the context of potential upregulation of osteoclast-mediated periodontal bone-resorption suggest the need for further investigation of this multifaceted molecule. In short, the pathophysiological role of Sema4D in periodontitis requires further study. Accordingly, attachment of the ligature to the maxillary molar of mice for 7 days induced alveolar bone-resorption accompanied by locally elevated, soluble Sema4D (sSema4D), TNF-α and RANKL. Removal of the ligature induced spontaneous bone regeneration during the following 14 days, which was significantly promoted by anti-Sema4D-mAb administration. Anti-Sema4D-mAb was also suppressed in vitro osteoclastogenesis and pit formation by RANKL-stimulated BMMCs. While anti-Sema4D-mAb downmodulated the bone-resorption induced in mouse periodontitis, it neither affected local production of TNF-α and RANKL nor systemic skeletal bone remodeling. RANKL-induced osteoclastogenesis and resorptive activity were also suppressed by blocking of CD72, but not Plexin B2, suggesting that sSema4D released by osteoclasts promotes osteoclastogenesis via ligation to CD72 receptor. Overall, our data indicated that ssSema4D released by osteoclasts may play a dual function by decreasing bone formation, while upregulating bone-resorption.