Modest changes in spacecraft charging conditions can lead to abrupt changes in the spacecraft equilibrium, from small positive potentials to large negative potentials relative to the space plasma; this phenomenon is referred to as threshold charging. It is well known that temporal changes of the space plasma environment (electron plasma temperature or density) can cause threshold charging. Threshold charging can also result from by temporal changes in the juxtaposition of the spacecraft to the environment, including spacecraft orbit, orientation, and geometry. This study focuses on the effects of possible changes in electron emission properties of representative spacecraft materials. It is found that for electron-induced emission, the possible threshold scenarios are very rich, since this type of electron emission can cause either positive or negative charging. Alternately, modification of photon-or ion-induced electron emission is found to induce threshold charging only in certain favorable cases. Changes of emission properties discussed include modifications due to: contamination, degradation and roughening of surfaces and layered materials; biasing and charge accumulation; bandstructure occupation and density of states caused by heat, optical or particle radiation; optical reflectivity and absorptivity; and inaccuracies and errors in measurements and parameterization of materials properties. An established method is used here to quantitatively gauge the relative extent to which these various changes in electron emission alter a spacecraft's charging behavior and possibly lead to threshold charging. The absolute charging behavior of a hypothetical flat, twodimensional satellite panel of a single material (either polycrystalline conductor Au or the polymeric polyimide Kapton™ H) is modeled as it undergoes modification and concomitant changes in spacecraft charging in three representative geosynchronous orbit environments, from full sunlight to full shade (eclipse) are considered.

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A highly durable optical disk has been developed for data archiving. This optical disk uses tellurium as the write layer and carbon as a dielectric and oxidation prevention layer. The sandwich style CTeC film was deposited on polycarbonate and silicon substrates by plasma sputtering. These films were then characterized with SEM, TEM, EELS, ellipsometry, ToF-SIMS, etc, and were tested for writability and longevity. Results show the films were uniform in physical structure, are stable, and able to form permanent pits. Data was written to a disk and successfully read back in a commercial DVD drive.

Loss of proppant from the near wellbore region of a fracture results in fracture pinch out and a noticeable decrease in well productivity. Downhole and surface equipment can be damaged when proppant flowback occurs as well. Resin coated proppant (RCP), fibers, deformable particles, resin on the fly, etc have been used to improve proppant pack stability. Selection of the appropriate proppant flowback control technology is made with consideration of engineering factors such as fluid compatibility issues, setting time, resistance to cycling stress-loading issues, and conductivity damage. The goal of the current work was to combine the beneficial features of mechanical proppant flowback control with chemical adhesive flowback control products. With mechanical features, the proppant pack stability is enhanced by blending fibers with proppant, thus increasing particle-particle interaction, and increasing the stability of proppant arches. This mechanism can enable aggressive flowback while providing an instantaneous, albeit a modest level of proppant flowback control. With the addition of an adhesive bonding mechanism to a mechanical flowback control material, the bicomponent material substantially increases proppant pack stabilization. Using a high temperature, high pressure proppant flowback control apparatus, we show the impact of particle bonding on the dosing required to achieve a specific level of proppant pack stability. We also show the impact of the flexible nature of bonded matrix on the proppant pack stability and tolerance to cyclic loading. A mechanistic proppant pack stability model was developed based on our experimental study. We discuss this model and its application towards the selection of the appropriate proppant flowback control technology for specific well conditions. We conclude the paper by discussing field cases of effective proppant flowback prevention techniques deployed as a result of model recommendation.

Described is a method for ultrasonically spraying thin films of carbon nanotubes that have been suspended in organic solvents. Nanotubes were sonicated in N-methyl-2-pyrrolidone or N-cyclohexyl-2-pyrrolidone (CHP) and then sprayed onto a heated substrate using an ultrasonic spray nozzle. The solvent was quickly evaporated, leaving a thin film of randomly oriented nanotubes. Unlike other methods of spraying nanotube films, this does not require removal of surfactant after spraying and is compatible with creating films of functionalized nanotubes. Film thickness was controlled by the spray time and films were sprayed with thicknesses between 10 and 500 nm. Single-walled, multiwalled, and functionalized multiwalled nanotubes were sprayed. Transparent conducting thin films prepared by spraying single-walled carbon nanotubes dispersed in CHP demonstrated similar sheet resistance (for a given optical transmittance) as those prepared by spraying aqueous polymer-based dispersions that required postdeposition polymer removal.