Effect of Substrate Morphology on Growth and Field Emission Properties of Carbon Nanotube Films

Carbon nanotube (CNT) films were grown by microwave plasma-enhanced chemical vapor deposition process on four types of Si substrates: (i) mirror polished, (ii) catalyst patterned, (iii) mechanically polished having pits of varying size and shape, and (iv) electrochemically etched. Iron thin film was used as catalytic material and acetylene and ammonia as the precursors. Morphological and structural characteristics of the films were investigated by scanning and transmission electron microscopes, respectively. CNT films of different morphology such as vertically aligned, randomly oriented flowers, or honey-comb like, depending on the morphology of the Si substrates, were obtained. CNTs had sharp tip and bamboo-like internal structure irrespective of growth morphology of the films. Comparative field emission measurements showed that patterned CNT films and that with randomly oriented morphology had superior emission characteristics with threshold field as low as ~2.0 V/μm. The defective (bamboo-structure) structures of CNTs have been suggested for the enhanced emission performance of randomly oriented nanotube samples

Evolutionary Consequences of Altered Atmospheric Oxygen in Drosophila melanogaster

Twelve replicate populations of Drosophila melanogaster, all derived from a common ancestor, were independently evolved for 34+ generations in one of three treatment environments of varying PO2: hypoxia (5.0–10.1 kPa), normoxia (21.3 kPa), and hyperoxia (40.5 kPa). Several traits related to whole animal performance and metabolism were assayed at various stages via “common garden” and reciprocal transplant assays to directly compare evolved and acclimatory differences among treatments. Results clearly demonstrate the evolution of a greater tolerance to acute hypoxia in the hypoxia-evolved populations, consistent with adaptation to this environment. Greater hypoxia tolerance was associated with an increase in citrate synthase activity in fly homogenate when compared to normoxic (control) populations, suggesting an increase in mitochondrial volume density in these populations. In contrast, no direct evidence of increased performance of the hyperoxia-evolved populations was detected, although a significant decrease in the tolerance of these populations to acute hypoxia suggests a cost to adaptation to hyperoxia. Hyperoxia-evolved populations had lower productivity overall (i.e., across treatment environments) and there was no evidence that hypoxia or hyperoxia-evolved populations had greatest productivity or longevity in their respective treatment environments, suggesting that these assays failed to capture the components of fitness relevant to adaptation

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion