Non-exclusionary input prices

This paper models a vertically-integrated provider that is a monopoly supplier of an input that is essential for downstream production. An input price that is “too high” can lead to inefficient foreclosure and one that is “too low” creates incentives for non-price discrimination. The range of non-exclusionary input prices is circumscribed by the input prices generated on the basis of upper-bound and lower-bound displacement ratios. The admissible range of the ratio of downstream to upstream price-cost margins is increasing in the degree of product differentiation and reduces to a single ratio in the limit as the products become perfectly homogeneous

Theory and it ab initio calculation of radiative lifetime of excitons in semiconducting carbon nanotubes

We present theoretical analysis and first-principles calculation of the radiative lifetime of excitons in semiconducting carbon nanotubes. An intrinsic lifetime of the order of 10 ps is computed for the lowest optically active bright excitons. The intrinsic lifetime is however a rapid increasing function of the exciton momentum. Moreover, the electronic structure of the nanotubes dictates the existence of dark excitons nearby in energy to each bright exciton. Both effects strongly influence measured lifetime. Assuming a thermal occupation of bright and dark exciton bands, we find an effective lifetime of the order of 10 ns at room temperature, in good accord with recent experiments.Comment: 12 pages, 3 figure

Extended performance solar electric propulsion thrust system study. Volume 4: Thruster technology evaluation

Several thrust system design concepts were evaluated and compared using the specifications of the most advanced 30 cm engineering model thruster as the technology base. Emphasis was placed on relatively high power missions (60 to 100 kW) such as a Halley's comet rendezvous. The extensions in thruster performance required for the Halley's comet mission were defined and alternative thrust system concepts were designed in sufficient detail for comparing mass, efficiency, reliability, structure, and thermal characteristics. Confirmation testing and analysis of thruster and power processing components were performed, and the feasibility of satisfying extended performance requirements was verified. A baseline design was selected from the alternatives considered, and the design analysis and documentation were refined. The baseline thrust system design features modular construction, conventional power processing, and a concentrator solar array concept and is designed to interface with the Space Shuttle

Toward Practical Non-Contact Optical Strain Sensing Using Single-Walled Carbon Nanotubes

Progress is reported in an emerging non-contact strain sensing technology based on optical properties of single-walled carbon nanotubes (SWCNTs). In this strain-sensing smart skin (“S4”) method, nanotubes are dilutely embedded in a thin polymer film applied to a substrate of interest. Subsequent strain in the substrate is transferred to the nanotubes, causing systematic spectral shifts in their characteristic short-wave infrared fluorescence peaks. A small diode laser excites a spot on the coated surface, and the resulting emission is captured and spectrally analyzed to deduce local strain. To advance performance of the method, we prepare S4 films with structurally selected SWCNTs. These give less congested emission spectra that can be analyzed precisely. However, quenching interactions with the polymer host reduce SWCNT emission intensity by an order of magnitude. The instrumentation that captures SWCNT fluorescence has been made lighter and smaller for hand-held use or mounting onto a positioning mechanism that makes efficient automated strain scans of laboratory test specimens. Statistical analysis of large S4 data sets exposes uncertainties in measurements at single positions plus spatial variations in deduced baseline strain levels. Future refinements to S4 film formulation and processing should provide improved strain sensing performance suitable for industrial application