No abstract

A new nanotube structural form is reported that resembles a double helix in multiwall boron nitride nanotubes (MW-BNNT) grown by a carbon-free chemical-vapor-deposition process as documented by evidence obtained by transmission electron diffraction and microscopy. The double-helix structure is found in MW-BNNTs exhibiting the same chirality in its different walls. The MW-BNNTs deviate from the structure of ideal nested coaxial cylindrical tubes. Most significantly, bright- and dark-field electron imaging reveals regular zigzag dark and bright spots on the side walls of the nanotubes. The repeating distance between the bright, or dark, spots is related to the chiral angle of the nanotube. Electron diffraction patterns recorded from individual nanotubes show additional diffraction spots belonging to the 201 zone axes, which are not allowed in a perfectly cylindrical nanotube. These additional diffraction spots become asymmetrical as smaller sections of the nanotube are probed. A series of diffraction patterns recorded along the tube axis showed that the imperfections giving rise to these spots move in a regular fashion around the circumference of the tube. It is shown that all experimental evidence supports the structure model of two helices; one is polygonal in cross section and highly crystalline and the other is circular and less ordered. It is further suggested that the double-helix structure is a result of stronger wall-wall interactions associated with the ionic bonding in boron nitride.

This study examined the effects of pretreatment with phencyclidine (PCP), a selective /V-methyl-D-aspartate (NMDA) antagonist, on behavioral and physiologic responses of the rat to experimental traumatic brain injury (TBI). For the behavioral experiments, rats were administered either saline or PCP (1.0, 2.0, or 4.0 mg/kg, intrapentoneally [IP] 15 min before TBI. Rats were ventilated as necessary following injury. The duration of acute suppression of several reflexes (pinna, corneal, righting, and flexion) and responses (escape, head support, and spontaneous locomotion) was recorded for up to 70 min after trauma. Longer-term behavioral assessments (beam walking, beam balance, inclined plane, ambulatory activity, and body weight) were made for up to 10 days after trauma. PCP did not significantly alter the duration of acute behavioral suppression. At a dosage of 1.0 mg/kg, PCP significantly attenuated all long-term deficits except beam walking. Maximal protection against beam walking deficits was provided by the 4.0 mg/kg dosage of PCP. Sixty-three percent of saline-treated animals died within 10 days after injury. For rats pretreated with 1.0, 2.0, and 4.0 mg/kg of PCP, 40%, 23%, and 33% died, respectively. In physiologic experiments, pretreatment with 4.0 mg/kg of PCP (IP) 15 min before injury did not significantly affect systemic cardiovascular responses, plasma glucose levels, or blood gas levels observed within 30 min after injury.While the possibility of effects mediated by other neurotransmitter systems cannot be excluded, these data suggest that NMDA agonist-receptor interactions contribute to the

This study seeks to explore whether electrochemical reduction of CO 2 (using current US average and future low carbon electricity) will become a viable route for the reuse of CO 2 for producing synthetic fuel. This paper presents the results of a technical and economic analysis conducted for a pathway that converts CO 2 released from fossil fuel-burning power plants to diesel fuel via electrochemical reduction of CO 2 to CO and the Fischer−Tropsch process. Currently achievable performance levels for CO 2 electrolyzers and the Fischer−Tropsch process were used to compute key metrics, including (i) cost of the synthetic fuel, (ii) well-to-gate CO 2 emissions, and (iii) overall energy efficiency. An engineering and economic model framework was developed for the investigation. The discounted cash flow analysis method was employed to calculate the cost of diesel fuel using a 500 MW power plant as the CO 2 source. The model takes into account capital expenditures as well as operating costs for the reactors and auxiliaries. The final cost varies from 3.80 to 9.20 dollars per gallon in 2010 US dollars depending on the projected level of technology achieved. The WTG CO 2 emissions vary from 180% (nearly twice) to a reduction of 75% compared to that of the business as usual scenario without carbon sequestration. The well-to-gate energy efficiency varies from 41 to 65%.